trouble with mcp23016 read and write

[sadlpx]

Attached is a peice of code i'm using to learn the MCP23016 io expander by microchip. So far i can write the data i want to GP0 (counting 0 > ff) no problem. now i only have two problemswhich i don't understand.

#1) when i do a read on GP1 the my led's tied to GP0 go off. I'm not writing to GP0 (or am i).

#2) I cannot read anything from GP1 except all 1's back. I hav eth epins tied to vcc (10K), I can pull the pins low with a jumper wire but no change in the data input.

I'm sure i missed something in the setup, and my code looks very much like the basic stamp artical and the Hitech C compiler listing

BUT it no work any ideas.


//////////////////////////////////////////////////////////////////
//
//
////////////////////////////////////////////////////////////////////////////////
#include <16F876.h>
#fuses HS,NOWDT,NOPROTECT,PUT,BROWNOUT,NOLVP
#device ICD=true
#use delay(clock=10000000) // value based on crystal

//Uses a Scott Edwards Electronics 4x20 Serial LCD module
#use rs232(baud=9600,parity=N,xmit=PIN_c4,rcv=PIN_B0,stream=RS232,invert,bits=8)

// Define project I2C communication pins
#define SCL_PIN PIN_A4
#define SDA_PIN PIN_A5
#use i2c(master, sda=SDA_pin, scl=SCL_pin)

// #include <MCP23016_1.c>
#include <BPP_420 LCD.C>

#define MCP23016_I2C_WRITE 0x40
#define MCP23016_I2C_READ 0x41

//=============================================
// #use standard_io(C)
// #use i2c(master,sda=PIN_C4,scl=PIN_C3)

// COMMAND BYTE TO REGISTER RELATIONSHIP : Table: 1-3 of Microchip MCP23016 - DS20090A
#define GP0 0x00
#define GP1 0x01
#define OLAT0 0x02
#define OLAT1 0x03
#define IPOL0 0x04 // INPUT POLARITY PORT REGISTER 0
#define IPOL1 0x05 // INPUT POLARITY PORT REGISTER 1
#define IODIR0 0x06 // I/O DIRECTION REGISTER 0
#define IODIR1 0x07 // I/O DIRECTION REGISTER 1
#define INTCAP0 0x08 // INTERRUPT CAPTURE REGISTER 0
#define INTCAP1 0x09 // INTERRUPT CAPTURE REGISTER 1
#define IOCON0 0x0A // I/O EXPANDER CONTROL REGISTER 0
#define IOCON1 0x0B // I/O EXPANDER CONTROL REGISTER 1

// BLOCK VARIABLE REGISTER

// ----------------------------------------------------------------------------


void write2Expander(unsigned char WriteAddress, unsigned char cmdByte, unsigned char lsbData) //, unsigned char msbData)
{
short int status;

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(lsbData); // First data byte pair as per command byte(cmd)
delay_us(20);
i2c_stop(); // stop condition
delay_us(50); // delay to allow write (12us)min.

}

// ----------------------------------------------------------------------------

int readExpander(unsigned int WriteAddress, unsigned int cmdByte)
{
int Data, lsbData, msbData;
short int status,count;

startRead:
count=0; // Initialize read attempts counter.

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_start();
delay_us(20); // restart condition
i2c_write(WriteAddress+1); // Send slave address and clear (R_/W)
delay_us(20);
/***/
lsbData = i2c_read(); // Data from LSB or MSB of register
delay_us(20);
i2c_stop(); // stop condition
delay_us(50); // delay to allow read (12us)min.
return(lsbData);
}




void main(void) {
int n, nn, o;

putc(3);
putc(12); // Clear LCD
putc(1);
// LCD_goto(0); // go to position 1
printf("I/O Tester");
write2Expander(MCP23016_I2C_WRITE, IODIR0, 0x00); // Direction of all data is output.
write2Expander(MCP23016_I2C_WRITE, IODIR1, 0xFF); // Direction of all data is input.
LCD_goto (20);

while(1) {

for (n=0; n<255; ++n) {
delay_ms(500);
nn = (n ^ 0xff);
write2Expander(MCP23016_I2C_WRITE, GP0, nn);
LCD_goto (20);
printf("\%03d ", n);

o = readExpander(MCP23016_I2C_WRITE, GP1);
LCD_goto (40);
printf("\%03d ",o);
}

[PCM programmer]

I have three comments:

1. You have altered the code from the examples shown in the AN245.
http://ww1.microchip.com/downloads/en/AppNotes/00245.zip
The sample code always writes or reads two bytes. You've changed
it to only handle one byte. Does that work ? All the text in the data
sheet always refers to two bytes:

[sadlpx]

I found the problem and posted working code in the code forum.

I rearranged the code as suggested by PCM programmer (thanks by the way) but was still having the inputs on GP0 turn off when i would read GP1. It was tough to find because it would work fine when i stepped through the code using debug (sometimes - depending on breakpoint).

Turns out the second I2Cstart within the read_MCP routine need more time. Increased delay from 20 to 50usec and the problem went away.

Hope this helps someone else.