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MCP23008

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aaronik19

Joined: 25 Apr 2011
Posts: 297

MCP23008

Posted: Mon Oct 10, 2011 3:12 pm

Dear All,

I am using about 4 IO Expander on one single I2C bus. The configuration is below:

Code:

// MCP008 REGISTERS
#define _IODIR 0x00
#define _IPOL 0x01
#define _GPINTEN 0x02
#define _DEFVAL 0x03
#define _INTCON 0x04
#define _IOCON 0x05
#define _GPPU 0x06
#define _INTF 0x07
#define _INTCAP 0x08
#define _GPIO 0x09
#define _OLAT 0x0A

void init_MCP23008() {
output_float(PIN_B1);
output_float(PIN_B0);
delay_ms(250);
}

void write_MCP23008(unsigned char WriteAddress, unsigned char cmdByte, unsigned char data)
{

i2c_start(); // start condition
delay_us(20);

i2c_write(WriteAddress); // Send slave address and clear (R/W_)
delay_us(20);

i2c_write(cmdByte); // Command byte and register to be written.
delay_us(20);

i2c_write(data); // First data byte pair as per command byte(cmd)
delay_us(20);

i2c_stop(); // stop condition
delay_us(50);
}

long int read_MCP23008(unsigned int WriteAddress, unsigned int cmdByte, unsigned int ReadAddress)
{
unsigned int data;

i2c_start(); // start condition
delay_us(20);

i2c_write(WriteAddress); // Send slave address and clear (R/W_)
delay_us(20);

i2c_write(cmdByte); // Command byte and register to be written.
delay_us(50);

i2c_start();
delay_us(20); // restart condition

i2c_write(ReadAddress); // Send slave address and clear (R_/W)
delay_us(20);

data = i2c_read(0); // Data from LSB or MSB of register
delay_us(20);

i2c_stop(); // stop condition

return(data);
}

and the main program is this:

Code:

#include "i2c.c"

#define MCP23008_write_add 0x40
#define MCP23008_read_add 0x41

void main()
{
write_MCP23008(0x01, _IODIR, 0x00);
write_MCP23008(0x02, _IODIR, 0xFF);
write_MCP23008(MCP23008_write_add, _IPOL, 0x00);
write_MCP23008(MCP23008_write_add, _IOCON, 0x00);
init_mcp23008();

while(1)
{

write_MCP23008(0x01,0x09, 0x01);
delay_ms(3000);
write_MCP23008(0x02,0x09, 0x02);
delay_ms(3000);
write_MCP23008(0x03,0x09, 0x03);
delay_ms(3000);
write_MCP23008(0x04,0x09, 0x04);

}

}

now I have the 4 IO Expander from address 0x01 to 0x04. When I am reading I am getting always 0xff. I am making something wrong? Thanks for your help to solve this issue. I am using PIC18F4550 with 20MHz crystal.

PCM programmer

Joined: 06 Sep 2003
Posts: 21708

Posted: Mon Oct 10, 2011 4:26 pm

Quote:

#define MCP23008_write_add 0x40
#define MCP23008_read_add 0x41

now I have the 4 IO Expander from address 0x01 to 0x04

The addresses of 0x40 and 0x41 are for your first MCP23008.

The sub-address of each separate MCP23008 chip is contained in the
control byte. It's defined by 3 bits (A0, A1, A2).
Download the MCP23008 data sheet:
http://ww1.microchip.com/downloads/en/DeviceDoc/21919d.pdf
Look at Figure 1-2 at the top right of page 8. You can see how if
the chip had a sub-address of 0 (A0, A1, A2 all connected to ground)
then the chip would have an i2c address of 0x40 (and 0x41 for reading).

So, you need to #define the control bytes for the other 3 MCP23008
chips. Look at the bit diagram and decide how to do it. Then write
the new #define statements. Then use those in your code to talk
to the specified chip.

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