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Microcontroller Programming » Connecting multiple buttons on the MCU

April 05, 2011
by lnino
lnino's Avatar

Hi at all.

I thought about wiring 10 Buttons, 3 LEDs, a servo and so on ... on my MCU.

As I tried, I was only able to get those things running on PORTC. The won't work when I put them on PORTB,D although I used the right syntax.

For instance:

// Enable the internal pullup on PB1 (the button)
PORTB |= (1<<PB1);

Is there a reason why this won't work or did I forgot something important.

If it's really not possible to use this ports for my buttons, how can I realise a selfmade keypad(0-9). Do I need two microcontrollers and how do they communicate with each other? Do I have to wire 0-5 on MCU1 and 6-9 on MCU2? But how do they know which button has been pressed on the other MCU?

Are there ports on the atmega168 which I can't use for buttons, leds, servos and so on? And why?

Is it possible the get 10 buttons or more running on a atmega168?

I am a little confused right now.

Maybe somebody can help me out.

April 05, 2011
by bretm
bretm's Avatar

Pin PB1 should work just like you described. What symptoms are you seeing that shows that it's not working?

All of the PORTnx pins can be used as general-purpose I/O pins. The bootloader that comes on Nerdkits chips puts PD0 and PD1 into serial-port mode and you have to disable that, and PC6 has to be the RESET pin unless you go through way more trouble than it's worth, and PB6/PB7 are for the crystal, etc., but the other PORTB and PORTD pins should be fair game.

So if you're not using the LCD you should be able to easily use PB0,1,2,3,4,5, PC0,1,2,3,4,5, and PD2,3,4,5,6,7, and PD0,1 if you disable the serial port.

April 06, 2011
by lnino
lnino's Avatar

Hi bretm,

thanks for your reply.

There was no error message, it was just not working. I will give it another try, maybe something wasn't wired correctly.

Perfect to know which ports I can use. Thanks for that.

So for my project I think I will have to remove my display to have enough ports available. Because I want to connect 10 Buttons, 2 Leds, 1 Servo and 1 Piezo Buzzer.

For the case I want to connect more items on a MCU which are physically possible, are there solutions? Is it possible to communicate with a second MCU?

April 06, 2011
by Rick_S
Rick_S's Avatar

You could use something like I am using in the I2C LCD project. I'm using a 16bit I2C port expander which effectively adds 16 I/O lines to the microcontroller. It could be used to handle all your buttons using only 2 lines from the micro (pins 27 & 28) That would leave you plenty of space for your other components.

Rick

April 06, 2011
by lnino
lnino's Avatar

Hi Rick,

thanks for your informational reply.

I was trying to find this port expander in Austria and Germany in the webshops, but I had no luck. What I found there was a MCP23016-I/SP. The datasheet is: HERE

Can I use this one instead of your MAX7318?

And how do I communicate with the ports of the port expander? When I want to wire a button on the expander, do I have to speek with the ports of the new expander directly? Or through pin 27 & 28?

Can you give me an code example?

And can I expand an expander? Or is this the maximum which I can get?

April 06, 2011
by Ralphxyz
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Hi Inino, yup you can use the MCP23016-I/SP. In fact I found a tutorial the other day using that chip for 16 buttons.

I'll see if I can find it again.

Ralph

April 06, 2011
by lnino
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Hi Ralph,

thanks for the reply.

Great that you just were in contact which that controller.

I am looking forward to your reply.

April 06, 2011
by Noter
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You can also communicate between mcu's using I2C. It's refered to as TWI (Two Wire Interface) of the ATmega but it's the same thing. There are a couple of examples buried in Rick's I2C LCD thread and the latest version of TWI master/slave code is in the Access Serial EEPROM using I2C thread. Between the two you should be able to find everything needed to communicate between two or more mcu's.

I prefer using additional mcu's over port expanders because of greater flexability and processing power as well as reduced hardware cost. As your projects get more complex and require more processing power you will run out of cycles on a single mpu regardless of the number of IO pins available. Likewise with flash, all the functionality on a single mcu means a much larger program.

Here is my current rats nest - one mpu driving three others via I2C slave master:

I2C master/slave example

April 06, 2011
by Ralphxyz
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Here is a Arduino I2C multi button project, which as Paul said in conjunction with Rick's and his code you will have most of what you need sitting in front of you.

There also a few Instructables.

Including one MIDI board that really looks interesting.

I sure like the idea of using multiple mcus now that's cool.

Ralph

April 08, 2011
by lnino
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Thank you guys.

April 17, 2011
by lnino
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Hi guys.

I have now read the posts and some links I found on google, but I have definately no clue how to get my MCP23016 working?

Maybe someone has experiences with that chip? Or someone can explain what I have to do?

Here are some links which I have found.

Link1 Link2

Thanks for your help.

April 17, 2011
by Ralphxyz
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What mcu are you planning to use? If you are using a ATmega168 or 328p you "should" be able to use Rick's code to talk between the 168 and the MCP23016 using I2C. Then you just need how to process input. The Arduino samples should get you going you just do not use wire.h. If you have the MCP23016 then try it throw a switch and see what happens using the samples that have been linked to so far.

Did you look at the Instructables? That MiDi board should have your answers.

Ralph

April 17, 2011
by lnino
lnino's Avatar

I think I have to take a second look on the post. :-)

April 21, 2011
by lnino
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I have now studied the Instructables. Now I know the theory about I2C. In spite of the link postings of Noter and Ralph I was not able to start writing a code for my I/O expansion.

I really have a thinking blockade and the arduino stuff is really confusing me.

Can someone give me a code example for my project?

In my project I have one atmega168 with some buttons, lcd and buttons on it. Because the ports ran out I want to connect a I/O Expander to the atmega168. On this I/O Expander I want to connect a button and a led. (Later more buttons)

Maybe someone can help me.

Datasheet

Thanks a lot.

April 21, 2011
by Noter
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I think that Rick's thread on the I2C LCD must be very close to what you need because he also used an I2C port expander. Did you see his source code near the top of the thread? http://www.nerdkits.com/forum/thread/1382/

April 21, 2011
by Ralphxyz
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This is Arduino code but you should be able to transpose the Arduino wire.h code to the TWI code used by Rick and Paul.

Rick and Paul use different libraries but they both make the native TWI calls.

Post your questions on transposing the wire.h it would be good to have that documented on the Nerdkits forum.

Ralph

April 23, 2011
by lnino
lnino's Avatar

I started another try and was able to get a little bid forward. But now I got stuck during the "make" process. When I type in make on the console it says: "Undefined Reference to 'i2c_int' and all other methods which are part of twimaster.c.

I downloaded the zip package from Fleury Link and copied 2 files(i2cmaster.h and twimaster.c) into the folder of my testprogram for the io expansion. So in my folder(io_expander) are now 4 files(i2cmaster.h,io_expander,twimaster.c and makefile).

Can someone tell me what I am doing wrong?

io_expander.c:

// io_expander.c
// for NerdKits with ATmega168

#define F_CPU 14745600

#include <stdio.h>

#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/pgmspace.h>
#include <inttypes.h>

#include "i2cmaster.h"

#include "../libnerdkits/delay.h"
#include "../libnerdkits/lcd.h"

#define DevMCP23016  0x20      // device address of IO_EXpander MCP23016 (0100 A2 A1 A0 --> 0100000 --> 0x20)

int main(void)

   {
     int i = 0;

    //Initialisierung IO Expander
     i2c_init();                             // initialize I2C library

     i2c_start_wait(0x20);                   // set device address and write mode
     i2c_write(0x06);                        // Auswahl IODIR (pointer)
     i2c_write(0x00);                        // DDR Port0 all output    
     i2c_write(0xFF);                        // DDR Port1 all input 0xFF = B11111111

     i2c_stop();                             // set stop conditon = release bus

         while(1)
         {

        i=i+1; 
        i2c_start_wait(0x20);

        i2c_write(0x00);
        i2c_write(i);

        i2c_stop(); 
        if (i > 255) i = 0;
        delay_ms(1000);

         }
    }

Makefile:

GCCFLAGS=-g -Os -Wall -mmcu=atmega168

LINKFLAGS=-Wl,-u,vfprintf -lprintf_flt -Wl,-u,vfscanf -lscanf_flt -lm
AVRDUDEFLAGS=-c avr109 -p m168 -b 115200 -P COM7
LINKOBJECTS=../libnerdkits/delay.o ../libnerdkits/lcd.o ../libnerdkits/uart.o

all:    io_expander-upload

io_expander.hex:    io_expander.c
    make -C ../libnerdkits
    avr-gcc ${GCCFLAGS} ${LINKFLAGS} -o io_expander.o io_expander.c ${LINKOBJECTS}
    avr-objcopy -j .text -O ihex io_expander.o io_expander.hex

io_expander.ass:    io_expander.hex
    avr-objdump -S -d io_expander.o > io_expander.ass

io_expander-upload: io_expander.hex
    avrdude ${AVRDUDEFLAGS} -U flash:w:io_expander.hex:a
April 23, 2011
by Ralphxyz
Ralphxyz's Avatar

Here is Rick's Makefile from his I2C LCD thread:

GCCFLAGS=-g -Os -Wall -mmcu=atmega328p 
LINKFLAGS=-Wl,-u,vfprintf -lprintf_flt -Wl,-u,vfscanf -lscanf_flt -lm
AVRDUDEFLAGS=-c avr109 -p m328p -b 115200 -P com1
LINKOBJECTS=../libnerdkits/delay.o ../libnerdkits/twimaster.o ../libnerdkits/I2C_lcd.o ../libnerdkits/uart.o

all:    tempsensor_I2C-upload

tempsensor_I2C.hex: tempsensor_I2C.c
    make -C ../libnerdkits
    avr-gcc ${GCCFLAGS} -o ../libnerdkits/twimaster.o -c ../libnerdkits/twimaster.c
    avr-gcc ${GCCFLAGS} -o ../libnerdkits/I2C_lcd.o -c ../libnerdkits/I2C_lcd.c
    avr-gcc ${GCCFLAGS} ${LINKFLAGS} -o tempsensor_I2C.o tempsensor_I2C.c ${LINKOBJECTS}
    avr-objcopy -j .text -O ihex tempsensor_I2C.o tempsensor_I2C.hex

tempsensor_I2C.ass: tempsensor_I2C.hex
    avr-objdump -S -d tempsensor_I2C.o > tempsensor_I2C.ass

tempsensor_I2C-upload:  tempsensor_I2C.hex
    avrdude ${AVRDUDEFLAGS} -U flash:w:tempsensor_I2C.hex:a

Notice you do not have any reference to twimaster in your Makefile

Such as Line 10 has:

avr-gcc ${GCCFLAGS} -o ../libnerdkits/twimaster.o -c ../libnerdkits/twimaster.c

He was nice enough to put this together to use with the tempsensor Nerdkit project outputting to the LCD using I2C.

So change your makefile and let's see what happens.

Ralph

April 23, 2011
by lnino
lnino's Avatar

Hi Rick,

I have added the line and a second one in the make file.

I also had to change the path of the i2cmaster.h in the Fleury Lib.

Now I can load my code into the MCU. But nothing happens.

My code should display the numbers 0-254 with the help of 8 LEDs in a loop with 1 second delay. Can somebody find an error?

April 23, 2011
by Noter
Noter's Avatar

The i2c address is 7 bits but shifted left 1 bit to make room for the read/write bit in the LSB position. So the byte looks like aaa aaaa w, w is 0 for write or 1 for read. So to write to device 0x20, 010 0000 0 or 01000000 or (0x20<<1)|0 or 0x40 in the start_wait routine.

I like your test program. I think Ralph may want to use it to debug his i2c port expander problem.

April 23, 2011
by Ralphxyz
Ralphxyz's Avatar

Inio, post your make file. Like Noter said I am trying to run your code also.

What pins do you have the leds on are you using switches for input?

Of course I am using the MAX7318 not the Microchip MCP23016 so I'll have to transpose the pins.

Are you still using the same code?

Ralph

April 24, 2011
by lnino
lnino's Avatar

@ Noter: Did I unterstand that right, that I have to use 0x40 when I want to write data and 0x41 when I want to read data?

In this case is read like input (button) and write like an output (led)?

Is my code correct, or do I have to change the device address?

@ Ralph: Of cource I will post my makefile.

Makefile of my project:

GCCFLAGS=-g -Os -Wall -mmcu=atmega168 
LINKFLAGS=-Wl,-u,vfprintf -lprintf_flt -Wl,-u,vfscanf -lscanf_flt -lm
AVRDUDEFLAGS=-c avr109 -p m168 -b 115200 -P COM9
LINKOBJECTS=../libnerdkits/delay.o ../libnerdkits/twimaster.o ../libnerdkits/lcd.o ../libnerdkits/uart.o

all:    io_expander-upload

io_expander.hex:    io_expander.c
    make -C ../libnerdkits
    avr-gcc ${GCCFLAGS} -o ../libnerdkits/twimaster.o -c ../libnerdkits/twimaster.c
    avr-gcc ${GCCFLAGS} ${LINKFLAGS} -o io_expander.o io_expander.c ${LINKOBJECTS}
    avr-objcopy -j .text -O ihex io_expander.o io_expander.hex

io_expander.ass:    io_expander.hex
    avr-objdump -S -d io_expander.o > io_expander.ass

io_expander-upload: io_expander.hex
    avrdude ${AVRDUDEFLAGS} -U flash:w:io_expander.hex:a

Makefile of libnerdkits:

GCCFLAGS=-g -Os -Wall -mmcu=atmega168

all: delay.o lcd.o uart.o lcd4x20ext.o twimaster.o

delay.o: delay.c
    avr-gcc ${GCCFLAGS} -o delay.o -c delay.c

lcd.o: lcd.c
    avr-gcc ${GCCFLAGS} -o lcd.o -c lcd.c

twimaster.o: twimaster.c
    avr-gcc ${GCCFLAGS} -o twimaster.o -c twimaster.c

uart.o: uart.c
    avr-gcc ${GCCFLAGS} -o uart.o -c uart.c

lcd4x20ext.o: lcd4x20ext.c
    avr-gcc ${GCCFLAGS} -o lcd4x20ext.o -c lcd4x20ext.c,

I copied the files i2cmaster.h and twimaster.c in my libnerdkits folder.

The code I used for this project I transposed from an arduino post. LINK

The code of my io_expander.c is still the same. I haven't changed it since I posted it.

The code seams really simple, but I don't know exactly what every line is doing. Maybe somebody can comment my code who understands it?

Here is the Datasheet of the MCP23016 Datasheet

I found some old leds which I used in my car some years ago. I have bought them with resistors because they have been connected to 12V. Do I also need the resistors in my project? I wanted to be secure.

I connected the LEDs to the Pins GP0.0-GP0.7 of my MCP23016.

And here is my environment: io_expander

April 24, 2011
by Rick_S
Rick_S's Avatar

Inino,

Looking at the Datasheet for the port expander you have, it appears that it's quite software compatable to the Maxim port expander I am using. Here's a couple of observations.

  1. As Noter said, your address is wrong for your device. The address of 0x20 is correct but your address byte also includes your read/write bit so your address of 0b0100000 becomes 0b01000000 for write and 0b01000001 for read or 0x40 and 0x41 respectively.
  2. I didn't read 100% of the datasheet for your expander but on a breif look-over it appears to use the same protocol as the Maxim I use. Therefore, the read/write routines from my I2C_LCD project would most likely work... Again I'm not 100% on that so take that for what it's worth.
  3. Looking at your setup, you have your LED resistors in the same row as your port expander pin and one leg of your LED's. The resistors will do nothing like that as both ends are connected to each other. To use the resistors (which I would recommend ones valued properly for 5V) you would have to use different rows for your LED's.

Rick

April 24, 2011
by Rick_S
Rick_S's Avatar

One other thing I just noticed about your wiring, you need to add pullup resistors to the I2C bus. Without them, it will not work. I use 4.7k resistors from SCL to 5v and SDA to 5v. It wouldn't hurt to put a bypass capacitor between the power and ground of your expander. You may be OK without it but it's a good habit to get into.

Rick

April 24, 2011
by lnino
lnino's Avatar

Thanks for your reply.

I have now changed the address of my MCP to 0x40. But there is still no light on my LEDs. But it can be the reason as you said with the pull up resistor.

You are completely right with the led and resistor setup. That is completely useless. :-) I will change it.

I do not understand why to use the read/write functions of your code. Isn't it the same in the i2cmaster.h? I think I do not understand. Maybe you could help me to understand it.

Your function uses the functions of the i2cmaster.h. What is the difference between this function and my code? Or is there more to use than this function?

void MAX7318_write(uint8_t address, uint8_t data) {

    i2c_start_wait((MAX7318_ADR)+(I2C_WRITE));  // Issue start on I2C bus in write mode

    i2c_write(address); // send the address of data to write

    i2c_write(data);    // send the data

    i2c_stop();         // Issue a stop on I2C bus

}

Thanks for your help.

April 24, 2011
by Rick_S
Rick_S's Avatar

Not really any difference, it just allows you to call a function to process the data rather than long-handing the transactions each time.

Rick

April 24, 2011
by Noter
Noter's Avatar

The datasheet has detailed information on I2C (two wire) as well as everything else on the ATmega*8's. Thumb thru chapter 21 and you'll see definition of the address bits discussed above and lots of other useful information including pull-up resistor values. Download a copy because you will need to reference it often as you implement various features of the chip.

There are different documents existing on the ATmega's but here is the one I use:

ATmega datasheet

April 24, 2011
by Ralphxyz
Ralphxyz's Avatar

I replicated Inio's setup using the MAX7318 port expander.

Now where is the address being called or used?

I see

#define DevMCP23016  0x20

But DevMCP23016 is never referenced again.

I am "trying" to compare to Rick's I2C tempsensor code he put together for me but I can not see where the address is being set in the tempsensor-I2C code either.

Also if 0x40 (read) and 0x41 (write) why not just do that in a #define?

#define deviceRead 0x40
#define deviceWrite 0x41

And then when you want to write just reference deviceRead or deviceWrite? Why bother appending the device address

 (deviceAddress << 1 + 0 or 1)

to make up 0x40 or 0x41?

Lots of questions but this is great I am actually starting to try to think like a programmer instead of a component assembler.

Ralph

April 24, 2011
by Noter
Noter's Avatar

Ralph, it doesn't matter that much, it's just a matter of style. As long as it works I would say your style is good.

I like to see the address value in its natural state so I would go for the style that shifts the value. I also try to remember to code in a fashion that resembles the documentation. SLA_W and SLA_R are defined/referenced in the datasheet.

#define I2C_DEV_ADDR 0X20
#define I2C_READ 0x01
#define I2C_WRITE 0x00
#define SLA_W = ((I2C_DEV_ADDR << 1) | I2C_WRITE);
#define SLA_R = ((I2C_DEV_ADDR << 1) | I2C_READ);

then

i2c_start_wait(SLA_W);

Now if the program gets large and I search the program for the address 0x20, I find it although I may find lots of them depending on the program. If I search the program for SLA_W or SLA_R, I find them and very quickly I am looking at the code I want to see.

But, it's not critical as long as the code works. Some organizations implement these types of styles into coding standards to keep code structure of all their programs similar thus increasing productivity of their programming staff.

April 24, 2011
by Ralphxyz
Ralphxyz's Avatar

Wow I am already up to questions of style. Thanks Paul, now, and again it might be style or just plain wrong, you have to consider the source.

instead of:

#define SLA_W = ((I2C_DEV_ADDR << 1) | I2C_WRITE);

why not:

#define SLA_W = I2C_DEV_ADDR + I2C_WRITE;

Wouldn't the append work?

I like the style of SLA_W what does SLA stand for? I know, I know I'll be re-re-re-re-reading the specsheet but thought I'd ask.

Ralph

April 24, 2011
by Noter
Noter's Avatar

That's not concatenation, it's addition. And your SLA (slave address) must already be shifted left to use that style so if you see I2C_DEV_ADDR somewhere as 0x40 you will have to shift right in your head to know it SLA 0x20.

April 24, 2011
by Ralphxyz
Ralphxyz's Avatar

What is concatenation then geesch back to the books.

Now this is cool I am actually seeing something on the digital analyzer that shows me what is going on, well actually it shows me what isn't going on:

Then more of the session:

So the Slave is not sending back a Acknowledgement.

Most likely because I still do not have the correct address somewhere!

I modified:

 i2c_start_wait(0x40);                   // set device address and write mode

What should I have changed if not i2c_start_wait()?

Ralph

April 24, 2011
by lnino
lnino's Avatar

Hi guys. I see the thread moved on a lot.

I was now able to change my project(resistors correct wired to the leds and resistors as pull up resistors).

I used 10K resistors as pull up resistor because I only had 3.3K and 10K. I wired the short end of the led to the resistor and the resistor is wired to GND. The long end of the Led is wired with a pin of the port expander.

I also put in a CLK and a capacitor.

Is the technical part okay?

After I had uploaded to code into the MCU, nothing happened. I changed to address of my port expander to x40.

What else do I have to do?

Maybe can I simplify my test project. Maybe it would be easier to turn on only one led by a button press? How can I realise that?

Or did I something wrong with my libs. Here is what I did with my lib:

1) Download of the zip file of Fleury.

2) Copied the files i2cmaster.h and twimaster.c into my libnerdkits folder.

3) Modified the makefile of the libnerdkits folder.

I inserted the following lines:

all: delay.o lcd.o uart.o lcd4x20ext.o twimaster.o

twimaster.o: twimaster.c
    avr-gcc ${GCCFLAGS} -o twimaster.o -c twimaster.c

4) I executed the make command and then I got the twimaster.o

5) And at last I changed the path in the file twimaster.c of the includefile "i2cmaster.h" to "../libnerdkits/i2cmaster.h".

io_expander.c:

// io_expander.c
// for NerdKits with ATmega168

#define F_CPU 14745600

#include <stdio.h>

#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/pgmspace.h>
#include <inttypes.h>

#include "../libnerdkits/i2cmaster.h"

#include "../libnerdkits/delay.h"
#include "../libnerdkits/lcd.h"

int main(void)

   {
     int i = 0;

    //Initialisierung IO Expander
     i2c_init();                             // initialize I2C library

     i2c_start_wait(0x40);                   // set device address and write mode
     i2c_write(0x06);                        // Auswahl IODIR (pointer)
     i2c_write(0x00);                        // DDR Port0 all output    
     i2c_write(0xFF);                        // DDR Port1 all input 0xFF = B11111111

     i2c_stop();                             // set stop conditon = release bus

         while(1)
         {

        i=i+1; 
        i2c_start_wait(0x40);

        i2c_write(0x00);
        i2c_write(i);

        i2c_stop(); 
        if (i > 255) i = 0;
        delay_ms(1000);

         }
    }

Here is a image of my current project.

alt image text

April 24, 2011
by Ralphxyz
Ralphxyz's Avatar

Hi lnino, as I said above I have replicated your project using the MAC7318 port expander.

I changed your code the same as you did.

As you can see from the digital analyzer images above the address is still not correct.

There has to be somewhere else that needs to be changed or the syntax is not correct.


Why do you have a crystal on the port expander? Or is that not your port expander.

If not what is it? It looks like it might be a microprocessor is it a PIC?

Ralph

April 24, 2011
by lnino
lnino's Avatar

This is my MCP23016. In the datasheet I saw a CLK and I thought I can put a crystal and a capacitor on it. Should I better remove them?

April 24, 2011
by Noter
Noter's Avatar

Ralph, what address in shown on the analyzer for your SLA_W? Looks like 0x10 to me. There is no 0x10 device out there to pull SDA low for an ack so it's a nak by default.

lnino, you need to read more in your datasheet, read it all. It says a resistor and capacitor need be connected to the clk input.

April 24, 2011
by Ralphxyz
Ralphxyz's Avatar

Yes Paul in 7bit mode it's 0x10 in 8bit mode it's 0x20.

I think I made the same changes as Inio:

#define DevMCP23016  0x20      // device address of IO_EXpander MCP23016 (0100 A2 A1 A0 --> 0100000 --> 0x20)
//#define DevMCP23016  0x40      // device address of IO_EXpander MCP23016 (0100 A2 A1 A0 --> 0100000 --> 0x20)

int main(void)

{
    int i = 0;

    //Initialisierung IO Expander
    i2c_init();                             // initialize I2C library

    i2c_start_wait(0x40);                   // set device address and write mode
    i2c_write(0x06);                        // Auswahl IODIR (pointer)
    i2c_write(0x00);                        // DDR Port0 all output    
    i2c_write(0xFF);                        // DDR Port1 all input 0xFF = B11111111

    i2c_stop();                             // set stop conditon = release bus

    while(1)
        {

        i=i+1; 
        i2c_start_wait(0x40);

        i2c_write(0x00);
        i2c_write(i);

        i2c_stop(); 
        if (i > 255) i = 0;
        delay_ms(1000);

        }
}

That's why I was asking where the address needs to be changed at.

 i2c_start_wait(0x40)

does not make any difference between

i2c_start_wait(0x20)

Both are seen as 0x20 at the Start.

Ralph

April 24, 2011
by lnino
lnino's Avatar

@ Noter: Thanks. I think I have to read it more intensive.

@ Ralph: I am looking forward that we are both getting our code running. I have good feeling. I will test some things on my code and when I was lucky I will post my code.

April 24, 2011
by Noter
Noter's Avatar

You changed the program, it must make a difference. If you don't see the a change on the analyzer then your compile, link, or upload must be failing and you are running the same old code over and over on the MCU. Make sure you have no error messages from any of the steps when you build the new version.

I see you have the 0x40 in both places in the program and that is correct so the new version must not be making it to the chip for some reason.

You could change it to something totally different like 0x7E in both places just to see what you get on the analyzer. If the program is getting compiled and loaded at least you should see something different.

April 24, 2011
by Rick_S
Rick_S's Avatar

Noter, I was just about to pop in and say the exact same thing... You beet me to it! Tongue in Cheek

Rick

April 24, 2011
by lnino
lnino's Avatar

I searched around the I-net and found some posts. As I see the wiring is a little bid different. They used a capacitor and a resistor on the CLK.

Link2 Link3

And here is a schematic I have found.

Image

April 24, 2011
by Ralphxyz
Ralphxyz's Avatar

Paul where do you see 0x40, I only see 0x20.

Is this code correct:

#define DevMCP23016  0x20      // device address of IO_EXpander MCP23016 (0100 A2 A1 A0 --> 0100000 --> 0x20)
//#define DevMCP23016  0x40      // device address of IO_EXpander MCP23016 (0100 A2 A1 A0 --> 0100000 --> 0x20)
#define I2C_DEV_ADDR 0x20
#define I2C_WRITE 0x00

int main(void)

{
    int i = 0;

    //Initialisierung IO Expander
    i2c_init();                             // initialize I2C library
    //i2c_start_wait(0x20);
    //i2c_start_wait(0x40);                   // set device address and write mode
    i2c_start_wait((I2C_DEV_ADDR << 1) | I2C_WRITE));
    i2c_write(0x06);                        // Auswahl IODIR (pointer)
    i2c_write(0x00);                        // DDR Port0 all output    
    i2c_write(0xFF);                        // DDR Port1 all input 0xFF = B11111111

    i2c_stop();                             // set stop conditon = release bus

    while(1)
        {

        i=i+1; 
        //i2c_start_wait(0x40);
        //i2c_start_wait(0x20);
        i2c_start_wait((I2C_DEV_ADDR << 1) | I2C_WRITE));
        i2c_write(0x00);
        i2c_write(i);

        i2c_stop(); 
        if (i > 255) i = 0;
        delay_ms(1000);

        }
}

I am still getting:

 START Write to Slave 0x20

Ralph

April 24, 2011
by Ralphxyz
Ralphxyz's Avatar

to answer my own question:

SLA as in "Slave Address" though it is never explicitly stated it is just sorta implied.

 SLA_W = Slave Address Write
 SLA_R = Slave Address Read

Ralph

April 24, 2011
by Noter
Noter's Avatar

I saw 0x40 being passed in the code you posted previously (about 2 1/2 hours ago).

Now you are using the 0x20 address and shifting it. 0x20<<1 = 0x40 so you are still calling i2c_start_wait with the correct value.

There is something wierd going on with your analyzer. Above in this thread it says "Writing to slave 0x20" and the byte is 00100000 but in Rick's LCD thread your analyzer pic says "W>>0x20" but with the byte 01000000 displayed. I don't know what is up with that. But no matter what it says, it shows 00100000 on your analyzer now and that is a byte of 0x20 meaning SLA of 0x10.

I don't think your changed code is loaded on the chip. Did you try changing from address of 0x20 to 0xFF and see if it makes a difference on the analyzer display? Are you for sure seeing the active signal on the analyzer and not viewing a saved buffer?

April 24, 2011
by Ralphxyz
Ralphxyz's Avatar

Darn the .hex and .o were not changing even with changes to the program.

I got new .hex and .o files and now all I get is a flat line on the digital analyzer.

I changed i2c_start_wait() to i2c_start_wait(0xFF);

I'll try to flip it back.

Ralph

April 24, 2011
by Ralphxyz
Ralphxyz's Avatar

Well when I flipped it back to i2c_start_wait(0x40);

I get 7 of the LEDs on bright!!

I am still getting a flat line high on SCL and SDA on the analyzer.

I guess this is progress :-)

Ralph

April 24, 2011
by Ralphxyz
Ralphxyz's Avatar

Now this is more like it:

Now to figure out why only 7 of 8 LEDs are lit and why they are on constantly it looks like they are supposed to cycle every second.

lnino what is your code suppose d to do?

Here is the code and Makefile that at least lights the LEDs (7 of 8). lnino, I would start over from scratch with your code. Use the original Nerdkit libnerdkit and do not make any changes to twimaster.c:

I am using a ATmega328P so the code has to be modified for the ATmega168:

/*
 *  io_expander.h
 *  
 */

// io_expander.c
// for NerdKits with ATmega168

#define F_CPU 14745600

#include <stdio.h>
#include <math.h>

#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/pgmspace.h>
#include <inttypes.h>

#include "../libnerdkits/delay.h"
#include "../libnerdkits/i2cmaster.h"
#include "../libnerdkits/I2C_lcd.h"
#include "../libnerdkits/uart.h"
#include "../libnerdkits/io_328p.h"

#define DevMCP23016  0x20      // device address of IO_EXpander MCP23016 (0100 A2 A1 A0 --> 0100000 --> 0x20)
//#define DevMCP23016  0x40      // device address of IO_EXpander MCP23016 (0100 A2 A1 A0 --> 0100000 --> 0x20)
#define I2C_DEV_ADDR 0x20
#define I2C_WRITE 0x00

int main(void)

{
    int i = 0;

    //Initialisierung IO Expander
    i2c_init();                             // initialize I2C library
    //i2c_start_wait(0x20);
    i2c_start_wait(0x40);                   // set device address and write mode
    //i2c_start_wait((I2C_DEV_ADDR << 1) | I2C_WRITE));
    //i2c_start_wait(0xFF);
    i2c_write(0x06);                        // Auswahl IODIR (pointer)
    i2c_write(0x00);                        // DDR Port0 all output    
    i2c_write(0xFF);                        // DDR Port1 all input 0xFF = B11111111

    i2c_stop();                             // set stop conditon = release bus

    while(1)
        {

        i=i+1; 
        i2c_start_wait(0x40);
        //i2c_start_wait(0x20);
        //i2c_start_wait((I2C_DEV_ADDR << 1) | I2C_WRITE));
        //i2c_start_wait(0xFF);
        i2c_write(0x00);
        i2c_write(i);

        i2c_stop(); 
        if (i > 255) i = 0;
        delay_ms(1000);

        }
}

And the Makefile:

GCCFLAGS=-g -Os -Wall -mmcu=atmega328p 
LINKFLAGS=-Wl,-u,vfprintf -lprintf_flt -Wl,-u,vfscanf -lscanf_flt -lm
AVRDUDEFLAGS=-c avr109 -p m328p -b 115200 -P /dev/cu.PL2303-0000101D
LINKOBJECTS=../libnerdkits/delay.o ../libnerdkits/twimaster.o ../libnerdkits/lcd.o ../libnerdkits/uart.o

ProjectName = io_expander

all:    io_expander-upload

io_expander.hex:    io_expander.c
        make -C ../libnerdkits
        avr-gcc ${GCCFLAGS} -o ../libnerdkits/twimaster.o -c ../libnerdkits/twimaster.c
        avr-gcc ${GCCFLAGS} -o io_expander.o -c io_expander.c
        avr-gcc ${GCCFLAGS} ${LINKFLAGS} -o io_expander.o io_expander.c ${LINKOBJECTS}
        avr-objcopy -j .text -O ihex io_expander.o io_expander.hex

io_expander.ass:    io_expander.hex
        avr-objdump -S -d io_expander.o > io_expander.ass

io_expander-upload: io_expander.hex
        avrdude ${AVRDUDEFLAGS} -U flash:w:io_expander.hex:a

I was making changes to the code but the .hex and .o files were not being updated so I had to remove them from the root folder in order to get the changes to take. Ralph

April 25, 2011
by lnino
lnino's Avatar

Hi Ralph. Thanks for your post.

As I see your working code is exactly as mine. You only have much more includes.

I think I will start the project from the beginning.

How did you use you i2c libs from Fleury? Where have you copied your files? Can you post or upload your i2c libs you have used for your project? Are maybe your complete project, so I can download and start it? So I can copy them into my libnerdkits folder and have the situation as you.

How looks your wiring at the current state? Can you post a foto of it?

Thanks a lot.

April 25, 2011
by lnino
lnino's Avatar

I forgot to ask how you implemented your libs from Fleury in your central makefile of the libnerdkits folder? Can you post this makefile?

Can you tell me step by step what you have done after you downloaded the zip file from Fleury. Maybe I did something wrong during the procedure.

Thanks

April 25, 2011
by Ralphxyz
Ralphxyz's Avatar

Hi Inino, first thing the reason the 8th LED did not light is/was because of a bad solder joint on the MAX7318 TSSOP-24 breakout board. The breakout board I used uses gull wing SMT headers, not through hole headers, plus I used low profile Swiss machined pin headers so I had to bend the rather fragile top pins 90˚ and some broke off before soldering them. Excuses excuses I know I should have rung out the breakout board before using it (I "thought" I had).

Anyway here are some shots:

I do not have a clean code package as I started using I2C three months ago when Rick (bless his heart) published his WII Nunchuck code.

And then DS3232 I2C Real Time Clock code.

And then Noter's I2C EEPROM code.

And then Rick's I2C LCD code which I could not get to work and then you started this thread with your real simple I2C port expander code so here we are.

The includes were from Rick's I2C LCD project code.

I have an io_expander folder under the Code folder (Nerdkits/Code/io_expander).

io_expander has:

 io_expander.c
 io_expander.h
 io_expander.o
 io_expander.hex
 Makefile

My IDE likes to use .h files so there is just a

#include "io_expander.h" in io_expander.c.

I have libnerdkits under the Code folder (Nerdkits/Code/libnerdkits)

delay.c
delay.h
delay.o
I2C_lcd.c
I2C_lcd.h
I2C_lcd.o
i2cmaster.h
io_328p.h
lcd.c
lcd.h
lcd.o
Makefile
twimaster.c
twimaster.o
uart.c
uart.h
uart.o

I had problems with io_expander.o and io_expander.hex NOT being updated when I changed the device address:

i2c_start_wait(0x40);

I had to delete them both manually before the address change took.

Look at the timestamp on your .o and .hex files to make sure they are being updated.

You do not need to modify the libnerdkits Makefile or change the path in twimaster.c

#include "i2cmaster.h" says to find i2cmaster.h "in the same folder as twimaster.c".

Now I'll modify your code to test the other 8 output pins and then see if I can get a switched input to fire a interrupt.

I need to test all of the pins on the port expander to see if there are other soldering problems and that is why I could not get Rick's I2C LCD code to work. It will not surprise me to find more soldering errors.

Thanks so much for starting this thread it has really helped me understand better what is going on with I2C and certainly taught me a lesson in I2C device addressing :-)

Ralph

April 25, 2011
by lnino
lnino's Avatar

Hi Ralph,

great to hear that you had success with your project.

I started now with my project at the beginning. And there are again starting problems.

In the folder "Nerdkits\Sample Source Code\io_expander" i have following files:

io_expander.c
Makefile

My includes of the file io_expander.c are looking like the following:

// io_expander.c
// for NerdKits with ATmega168

#define F_CPU 14745600

#include <stdio.h>

#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/pgmspace.h>
#include <inttypes.h>

#include "../libnerdkits/i2cmaster.h"

#include "../libnerdkits/delay.h"
#include "../libnerdkits/lcd.h"

The makefile of my project looks like this:

GCCFLAGS=-g -Os -Wall -mmcu=atmega168 
LINKFLAGS=-Wl,-u,vfprintf -lprintf_flt -Wl,-u,vfscanf -lscanf_flt -lm
AVRDUDEFLAGS=-c avr109 -p m168 -b 115200 -P COM9
LINKOBJECTS=../libnerdkits/delay.o ../libnerdkits/twimaster.o ../libnerdkits/lcd.o ../libnerdkits/uart.o

all:    io_expander-upload

io_expander.hex:    io_expander.c
    make -C ../libnerdkits
    avr-gcc ${GCCFLAGS} -o ../libnerdkits/twimaster.o -c ../libnerdkits/twimaster.c
    avr-gcc ${GCCFLAGS} -o io_expander.o -c io_expander.c
    avr-gcc ${GCCFLAGS} ${LINKFLAGS} -o io_expander.o io_expander.c ${LINKOBJECTS}
    avr-objcopy -j .text -O ihex io_expander.o io_expander.hex

io_expander.ass:    io_expander.hex
    avr-objdump -S -d io_expander.o > io_expander.ass

io_expander-upload: io_expander.hex
    avrdude ${AVRDUDEFLAGS} -U flash:w:io_expander.hex:a

The zip file of Fleury consists following files:

group__pfleury__i2cmaster.html
i2cmaster.h
i2cmaster.S
makefile
makefile.i2cmaster
makefile.twimaster
test_i2cmaster.c
twimaster.c

Then I copied two files (i2cmaster.h and twimaster.c) into the folder "Nerdkits\Sample Source Code\libnerdkits". I downloaded the libnerdkits folder untouched from the nerdkits website again, so there is no modification.

When use the make command I get an error message:

F:\Entwicklung\Microcontroller\Nerdkits\Sample Source Code\io_expander>make
make -C ../libnerdkits
make[1]: Entering directory `F:/Entwicklung/Microcontroller/Nerdkits/Sample Sour
ce Code/libnerdkits'
avr-gcc -g -Os -Wall -mmcu=atmega168  -o delay.o -c delay.c
avr-gcc -g -Os -Wall -mmcu=atmega168  -o lcd.o -c lcd.c
avr-gcc -g -Os -Wall -mmcu=atmega168  -o uart.o -c uart.c
make[1]: Leaving directory `F:/Entwicklung/Microcontroller/Nerdkits/Sample Sourc
e Code/libnerdkits'
avr-gcc -g -Os -Wall -mmcu=atmega168  -o ../libnerdkits/twimaster.o -c ../libner
dkits/twimaster.c
../libnerdkits/twimaster.c:12:23: error: i2cmaster.h: No such file or directory
make: *** [io_expander.hex] Error 1

An additional question: How do I get the twimaster.o? Do I get it with the makefile of my project?

Normally when I write my own lib I make a test.c and a test.h file and I customize the makefile of the libnerdkits folder. When I start after that the make command of in my libnerdkits the test.o is generated.

Is this a wrong way?

Can you tell me what I do wrong? Or can you give me your libs which are necessary for this project?

This is making me crazy. :-)

April 25, 2011
by Noter
Noter's Avatar

The error is from twimaster.c. It is looking for i2cmaster.h in the avr lib directory. I would change the following in twimaster.c -

#include <i2cmaster.h>

to

#include "i2cmaster.h"

so it will look in it's own directory instead of the avr lib directory.

April 25, 2011
by lnino
lnino's Avatar

Hi Noter. Thanks for you reply.

Now the make command works. The last time i changed the value to ../libnerdkits/i2cmaster.h -- I think this might have been the same.

But my leds are still not lighing up.

My code is completely the same as the code of Ralph. Maybe there is a wiring problem after all?

I have added a resistor and a capacitor like I saw in some tutorials which I posted some posts before. I also removed the new parts, but there was also no light.

Any ideas?

IO Expander

April 25, 2011
by Noter
Noter's Avatar

Using ../libnerdkits means to go up one level (../) to the parent directory and then down into the libnerdkits directory. Since twimaster.c is already in the libnerdkits directory there is no need to go up and back down to the same place so you can leave it out in this case.

I'd like to see where that blue wire goes to your nerdkit mcu. Also, what value of resistor and capacitor did you put on the CLK pin? And, what values of resistors are you using for pull-ups on the I2C lines?

April 25, 2011
by lnino
lnino's Avatar

Maybe I found a mistake on my wiring.

It is recommended in the datasheet to use a 33pF capacitor and a 3.9K resistor and the CLK. Because I do not have values I used other values(0,1microF and 3.3k) instead.

Maybe because of that the clock is not working right?

I have also find some tutorials and howtos for the pull up resistor on the MCP23016. I found values between 1.8K and 10K.

In this project I used a 10K resistor for the pull up.

April 25, 2011
by Noter
Noter's Avatar

A .1uf is 100000pf so that probably isn't so good for the MCP23016 clock. My guess is that would keep things from working. Better get some pf caps.

Most examples use a 4.7k ohm resistor for the I2C pullup. I have used 2.2k with more slaves and an analyzer connected but a 4.7k is best for your setup.

Then be sure SDA and SCL are going to the correct pins on the MCU.

That's all I can think of for now.

April 26, 2011
by lnino
lnino's Avatar

Thanks for your post Noter.

I gonna buy some right stuff and will give it then another try.

Thanks to all for helping me on my project.

April 26, 2011
by Ralphxyz
Ralphxyz's Avatar

lnino, try signing up at Mouser.com for their sample program they will send you samples like the Max7318 free.

They probable have a distribution center in Germany.

Ralph

April 26, 2011
by lnino
lnino's Avatar

Hi Ralph.

This is a good information.

I am now signed in.

How do I get to the sample program of the site?

April 27, 2011
by Rick_S
Rick_S's Avatar

Inino, I'll jump in here. I think Ralph meant maxim-ic.com. You can also get samples from TI, Analog Devices, MicroChip, and I'm sure others. I've personally gotten many samples from maxim-ic, a few from Analog Devices, and am attempting some from Microchip right now.. (just waiting approval of an order). Maxim's sample policy is very hobbyist friendly.

Rick

May 28, 2011
by lnino
lnino's Avatar

Hi at all.

After some time where I had no time for working on my MCU I am back right now.

In the meanwhile I bought a lot of stuff for my project(including the resistors and capacitors which I need for the port expander).

I changed now the resistors on the MCP3016 to 3.9K and the capacitor to 33pF. I have also changed the value of the pull up resistors to 4.7k.

And what a result: "It worked!". Awesome.

Really big thanks to Ralph, Rick and Noter all other people who helped me on this project.

I have now changed my code to have a button pressed on my MCU which should turn on a led on my port expander. That works great either.

Now I was thinking about to try it the other way round. Pressing a button which hangs on my port expander which should turn on a led on my MCU. But I have no clue how to change my code for doing this. Any ideas?

I have also a little phenomenon when I use my code counting from 0 to 255. My code hang after some time. When I start my program the leds are flashing and counting nice. But after some time it stops. Always on a different position.

And the second thing which I found out is: When I have my batterie connected and I push my button for lighting all LEDs on the port expander they light bright. When I disconnect the batterie the are still lighting but not so bright. When I disconnect the red wire between the two breadboards the light goes off.

Why this happens? Is this because of the capacitors which store the current? Or wrong capacitors?

Link to the MCP3016 Datasheet -> Datasheet

io_expander.c:

// io_expander.c
// for NerdKits with ATmega168

#define F_CPU 14745600

#include <stdio.h>

#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/pgmspace.h>
#include <inttypes.h>

#include "../libnerdkits/i2cmaster.h"

#include "../libnerdkits/delay.h"
#include "../libnerdkits/lcd.h"

int main(void)

   {
     int GP0_0 = 1;
     int GP0_1 = 2;
     int GP0_2 = 4;
     int GP0_3 = 8;
     int GP0_4 = 16;
     int GP0_5 = 32;
     int GP0_6 = 64;
     int GP0_7 = 128;
     int GP0_all = 255;

     // Button as Input PB1
     DDRB &= ~(1<<PB1);

     // turn on the internal resistors for the pins
     PORTB |= (1<<PB1); // turn on internal pull up resistor

    //Initialisierung IO Expander
     i2c_init();                             // initialize I2C library

     i2c_start_wait(0x40);                   // set device address and write mode
     i2c_write(0x06);                        // Auswahl IODIR (pointer)
     i2c_write(0x00);                        // DDR Port0 all output    
     i2c_write(0xFF);                        // DDR Port1 all input 0xFF = B11111111

     i2c_stop();                             // set stop conditon = release bus

         while(1)
         {

            if(!(PINB & (1<<PB1))) // When Button is pressed
              { 
                delay_ms(120);

                i2c_start_wait(0x40);

                i2c_write(0x00);
                i2c_write(GP0_all);

                i2c_stop();             
              }
         }
    }

picture

May 28, 2011
by lnino
lnino's Avatar

Datasheet of Leds is here Link

May 28, 2011
by Ralphxyz
Ralphxyz's Avatar

Inino said:

[quote] "When I disconnect the batterie the are still lighting but not so bright. When I disconnect the red wire between the two breadboards the light goes off." [/quote]

Inino, you should not have the battery connected plus the USB red wire to the + rail connected at the same time.

Do an either one or the other but not both.

The battery life will not be long using a battery so it might be better to use the USB power or a wall wart.

Also I get enough voltage from the yellow USB wire to light leds directly off the mcu I do not know if they would light across the port expander.

I never got to using a switch on the Port Expander so I hope you get it working I think some of the links quoted above have some button code.

Ralph

May 29, 2011
by lnino
lnino's Avatar

Hi Ralph,

thanks for your reply. That was exactly the problem, that I used the batterie AND the + of the USB cable.

I will try to find out how I can use the port expander to get an input.

Is the resitor value the right one on my new red leds(see my picture above)? I took the one from my bigger green transparent leds.

May 31, 2011
by lnino
lnino's Avatar

I tried to traspose the arduino code of this post post to get a button as an input working on my port expander, but I was not able to figure out how code works or what the code should do.

Maybe someone can help me to understand?

July 12, 2012
by Ralphxyz
Ralphxyz's Avatar

Hey Inio, now that you are back from vacation, I have been meaning to ask you if you ever got the Port Expander input working?

Thanks to your code and all of the great help on this thread I got the output working but never the input.

Of course this is from a year ago but maybe you can find your code for the working input.

Of course I am leaning toward using Noter's (whom I really miss) method of using the ports on a slave mcu instead of the port expander.

Ralph

July 12, 2012
by lnino
lnino's Avatar

Hi Ralph,

i am Sorry to say that i was Never able to get the Input Working. But I will try again. I am reaching Project sizes where it would be really helpful to have more Pins. I will keep you up to Date when I Start a New try. Thanks for your Support.

March 28, 2013
by lnino
lnino's Avatar

Hi Ralph,

I am still working on the project to get the input working on the MCP23016.

Here is a maybe functional code I wrote which the help of many forum threads and websites. I put some really good ideas together which I found.

I had no time to test it, but maybe the next days. Maybe its useful for you.

#define F_CPU 14745600
#include <stdio.h>
#include <avr/io.h>
#include <avr/pgmspace.h>
#include <inttypes.h>
#include <util/delay.h>

#include "../libnerdkits/i2cmaster.h"

#define MCP23016   0x40

voaltile uint8_t inputregister;

void SendData(uint8_t, uint8_t);
uint8_t ReadData(uint8_t);

int main(void)

   {   
    i2c_init();                             // initialize I2C library

   SendData(0x06,0x00);               // Sets all Ports on GP0 to Output
   SendData(0x07,0xFF);               // Sets all Ports on GP1 to Input

       while(1)
       {
           inputregister = ReadData(0x06);                 // Reads Input on GP1

          if(inputregister == 0b00000010 ) // When Button GP1.1 is pressed
           { 
                    // Do something         
           }

          elseif(inputregister == 0b00000100 ) // When Button GP1.2 is pressed
           { 
                     // Do something         
           }

          elseif(inputregister == 0b00001000 ) // When Button GP1.3 is pressed
           { 
                      // Do something         
           }
       }
   }

uint8_t ReadData(uint8_t command)
{ 
  uint8_t  data;

  i2c_start_wait(MCP23016 | 0x00);      // Write
  i2c_write(command);               // GP0 or GP1
  i2c_stop();

  i2c_rep_start(MCP23016 | 0x01);      // Read
  data = i2c_readNak();
  i2c_stop();

  return data;
}

void SendData(uint8_t command, uint8_t port)
{
   i2c_start_wait(MCP23016);         // set device address and write mode
   i2c_write(command);
   i2c_write(port);
   i2c_stop();
}

I also found a code which makes it more readable to send write commands. Because the thread I found was in dutch I translated it into englisch and adapted it to work with the nerdkit and the fleury I2C lib. Hard stuff with google translator. :-) But it worked. I have also put some other code parts I found in the web to this code. So this code is a summary of all good things I found on my search with MCP23016. This code is tested and works great. I hope the examples and explanations might help.

// io_expander.c
// for NerdKits with ATmega168

#define F_CPU 14745600

#include <stdio.h>

#include <avr/io.h>
#include <avr/pgmspace.h>
#include <inttypes.h>
#include <util/delay.h>

#include "../libnerdkits/i2cmaster.h"

#define MCP23016    0x40

// MCP23016 command byte to register relationship
 #define GP0        0x00  // Data Port, Current status of pins
 #define GP1        0x01  // Data Port, Current status of pins
 #define OLAT0      0x02  // Output Latch, Current status of latched pins
 #define OLAT1      0x03  // Output Latch, Current status of latched pins
 #define IPOL0      0x04  // Input polarity, 0-normal, 1-inverted
 #define IPOL1      0x05  // Input polarity, 0-normal, 1-inverted
 #define IODIR0     0x06  // IO Direction, 0-output, 1-input
 #define IODIR1     0x07  // IO Direction, 0-output, 1-input
 #define INTCAP0    0x08  // Interrupt capture, Read-Only, value of port that generated the interrupt
 #define INTCAP1    0x09  // Interrupt capture, Read-Only, value of port that generated the interrupt
 #define IOCON0     0x0A  // IO Expander Control, Sampling frequency ofGP pins, 0-normal, 1-fast
 #define IOCON1     0x0B  // IO Expander Control, Sampling frequency ofGP pins, 0-normal, 1-fast

void SendData(uint8_t, uint8_t);

int main(void)

   {

    // #################################### //
    // ## Initialisation of the MCP23016 ## // 
    // #################################### //

    i2c_init();                             // initialize I2C library

    SendData(0x06,0x00);                    // Sets all Ports on GP0 to Output
    SendData(0x07,0xFF);                    // Sets all Ports on GP1 to Input

    /*
    Explanation:
    A command which is sent to the MCP23016 consists of 2x8 Bit.
    The first 8 bit defines the command which is sent to the MCP23016. -- f.i. (0x06,...) for GP0, (0x07,...) for GP1
    The second 8 bit defines the ports of the MCP23106 -- f.i. (...,0x04) = (...,00000100) -> Port 2 is meant.

    Examples:
    SendData(0x06,0x03);                    // 0x03 = 00000011      Sets Port0 and Port 1 on GP0 to Output - Rest to Input
    SendData(0x07,0x08);                    // 0x08 = 00001000      Sets Port3 on GP1 to Output - Rest to Input
    */

         while(1)
         {

         SendData(0x00,0x04);               //Sets GP0.2 to High, Rest to Low

         /*
         Explanation commands:
         (0x01)=00000001 -> GP1
         (0x00)=00000001 -> GP0

         Explanation ports:
         (0x04) = (00000100) -> GPx.2

         Example:
         SendData(0x00,0x09);               // 0x09 = 00001001      Sets GP0.0 and GP0.3 to High, Rest to Low
         */

         }
    }

void SendData(uint8_t command, uint8_t port)
{
    i2c_start_wait(MCP23016);           // set device address and write mode
    i2c_write(command);
    i2c_write(port);
    i2c_stop();
}

The Original Code is here: Dutch Code

March 28, 2013
by Ralphxyz
Ralphxyz's Avatar

Wow lnino, this is great, not only translated from the Dutch but from Arduino Sketch code also.

Ralph

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