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j_s_connell
Joined: 02 Feb 2004
Posts: 17
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| has anyone used the new mcp23008 port expander? |
 Posted: Fri Apr 22, 2005 5:56 pm |
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I cannot get this chip to respond. I am using a pic18f2445 and the newest ccs. It never does anything, but if i put a similiar chip (pcf8547) on the i2c bus with a different address, the new chip works fine. Also if i read any port on the chip, i get back a value of 0xFF, which should not be the case.
So I think my problems are not i2c bus related, maybe bad software?
Here is the code I am using:
mcp23008.c:
| Code: |
#define MCP23008_I2C_WRITE 0x40
#define MCP23008_I2C_READ 0x41
// 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 write_MCP(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_MCP(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);
ldata = i2c_read(); // Data from LSB or MSB of register
delay_us(20);
i2c_stop(); // stop condition
return(data);
}
// ----------------------------------------------------------------------------
void init_mcp()
{
output_float(PIN_B0);
output_float(PIN_B1);
// Wait for MCP23016 Expander Device to power-up.
delay_ms(250);
// Set-up selected I/O expander unit
write_MCP(MCP23008_I2C_WRITE, _IPOL, 0x00); // NonInvert all input polarities if active low
write_MCP(MCP23008_I2C_WRITE, _IOCON, 0x00); // IARES(1) to max. activity detection time.
write_MCP(MCP23008_I2C_WRITE, _IODIR, 0x00); // Direction of all data is output.
// write_MCP(MCP23008_I2C_WRITE, _OLAT, 0xFF); // Update o/p latch that controls the output.
// write_MCP(MCP23008_I2C_WRITE, _GPPU, 0xFF); // Enable pullups
}
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And here is my test code:
| Code: |
#include <18f2455.h>
#FUSES HS,MCLR,PUT,NOWDT,NOBROWNOUT,NODEBUG,NOIESO,NOLVP,NOWRT,NOWRTD,NOFCMEN
#use delay(clock=16000000)
#use i2c(MASTER, SDA=PIN_B0, SCL=PIN_B1, FAST, FORCE_HW)
// #use i2c(MASTER, SDA=PIN_B0, SCL=PIN_B1)
#include "mcp23008.c"
void main(){
init_mcp();
while(1){
write_mcp(0x40, _OLAT, 0xF0);
}
}
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If anyone has any ideas, i would be greatful for some advice. |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Fri Apr 22, 2005 8:09 pm |
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I didn't check your entire program, but I scanned it and spotted one
error. Remember that in i2c, you always have to do a "NAK" on the
last read. With CCS, you do this by giving a 0 parameter to the
i2c_read() function. You need to change your code, as shown in
bold below.
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);
ldata = i2c_read(0); // Do a NAK on the last i2c read
delay_us(20);
i2c_stop(); // stop condition
return(data);
} |
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