Problem with i2c on pic16f88

[tbsnake2]

I am trying to do software i2c using scl=A3, SDA=A4. When an i2c write command is executed, it seems to hang. I recognize this part has a built in hardware i2c, which I am not implementing because of other reasons. The code below is a test routine for getting the i2c to work. I have been playing with turning off/on various hardware functions in order to get it to work. Could be wrong, but it seems like the TRIS settings are incorrect inside the i2c_write code. The i2c function you see below is a result of cutting it out of the memory chip driver to get down to the problem.

#include "C:\robspicc\ASTF88\ASTF88.h"
#include "C:\robspicc\astmemtest\at24c1024.c"
void Fast_Blink();
int mem_page;

void main()
{
long int a;
long int b;
// PORTB = 0; //HARDWARE CONTROL
// set_tris_A (0xFF);
setup_adc(ADC_OFF);
setup_comparator(NC_NC_NC_NC);
port_b_pullups(FALSE);
setup_spi(FALSE);
SETUP_CCP1(CCP_OFF);
enable_interrupts(GLOBAL);
SETUP_SPI(SPI_SS_DISABLED);
setup_counters(RTCC_INTERNAL,RTCC_DIV_2);
setup_timer_1(T1_INTERNAL | T1_DIV_BY_4);
setup_timer_2(T2_DIV_BY_16,224,16);
setup_timer_0(RTCC_DIV_256 | RTCC_INTERNAL);
enable_interrupts(INT_EXT);
mem_page = 0;
// Fast_Blink();
output_high(PWR);
output_high(SCL);
output_high(SDA);
init_ext_eeprom();
while(1){
a=a+1;
delay_ms(1000);
Fast_Blink();
i2c_start();
i2c_write(0xAA);
i2c_stop();
// WRITE_EXT_EEPROM(mem_page,a,b);
// delay_ms(1000);
// printf("%d",READ_EXT_EEPROM(mem_page,a));

}
}

#include <16F88.h>
#device adc=10
#use delay(clock=38400)
//#fuses LP,NOWDT,NOBROWNOUT,NOLVP,NOMCLR
#use rs232(baud=300,parity=N,xmit=PIN_B5,rcv=PIN_B2,bits=8)
#use i2c(Master,sda=PIN_A4,scl=PIN_A3,slow)
#define PING PIN_A1
#define S_DOUT PIN_B1
#define S_SCLK PIN_B3
#define S_DIN PIN_B6
#define PWR PIN_B4
#define OSCPWR PIN_B7
#define IRRXPWR PIN_A0
#define LED PIN_B0
#define SDA PIN_A4
#define SCL PIN_A3
#byte PIR1 = 0x0c
#byte PORTB = 0x06
#byte PORTA = 0x05

[Ttelmah]

So, what is actually 'wrong', when you try a more complete code sequence (write a byte, and then read it).
The TRIS operation, in software I2C, is 'non intuitive'. The code toggles the TRIS bits, to simulate an open collector drive. Hence the data bit for the two lines wll be set to '0', and then when a '0' is to be sent, the TRIS bit will be set to an output, and when a '1' is to be sent, the TRIS bit will be set to an input.
The code as written will do nothing, except send a bit pattern down the data line, since you are just sending a 'control' byte, and then stopping. Remember you must have resistive pull-ups on both lines. If this is not present, or inadequate, on the data line, it will hang the code, where it looks for the 'ACK' at the end of the write operation. This sounds suspiciously like your problem. The same will apply, if the chip is not being properly addressed.
Also remember on a 'read', you need to use the 'NACK' option on the last transfer.

Best Wishes

[tbsnake2]

the problem is that I am not seeing the data at all on the SDA or SCL lines. The single i2c_write was put in as I was trying to get something to appear on the SDA and SCL lines. (In other words, the lines are always at a '1' on the scope - they do not change).

Also doing a routine which toggles between output_high and output_low on the same lines I am doing the software sda and scl DOES work.

What is suspicious is that I use almost identical code on a 16f688 for another project and it works fine.

[Ttelmah]

[Guest]

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