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jk726
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| PIC to PIC communication using i2c |
 Posted: Fri Jul 31, 2009 12:49 am |
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Hi.
Using 2 microcontrollers, I want to make a system in which
first PIC gives instructions via i2c interface to the second PIC
and based on the instruction given, the second PIC displays data via LCD.
Thus,
1st PIC ---(1byte(for RS)+1byte(for character or instruction))-->2nd PIC---->LCD display
After getting into more complex coding, I wanted to see if I can send 2 bytes via I2c.
After reading some posts and help file, I tested following code.
First, I tried to see if I could send one byte using following code.
Master:
| Code: |
#include<16F886.h>
#include<def_16f886.h>
#fuses intrc_io, noprotect
#use delay(clock = 4000000)
#use i2c(master, sda = pin_c4, scl = pin_c3)
void main(void){
osccon = 0x41;
while(1){
delay_ms(1000);
i2c_start();
i2c_write(0xa0);
i2c_write('A');
i2c_stop();
}
}
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Slave:
| Code: |
#include<16f886.h>
#include<def_16f886.h>
#use delay(clock = 4000000)
#include<flex_lcd.h>
#fuses intrc_io, noprotect, debug
#use delay(clock = 4000000)
#use i2c(slave, sda = pin_c4, scl = pin_c3, address = 0xa0)
int8 address = 0;
int8 buffer[5] = {0, 0, 0, 0, 0};
int8 incoming = 0;
int8 first_byte = 0;
int8 second_byte = 0;
int8 state = 0;
#int_ssp
void ssp_interupt ()
{
state = i2c_isr_state();
if(state < 0x80) //Master is sending data
{
incoming = i2c_read(0);
}
if(state == 0x80) //Master is requesting data
{
i2c_write(buffer[address]);
}
LCD_gotoxy(1,1);
delay_ms(1);
lcd_putc(incoming);
}
void main(void){
enable_interrupts(int_ssp);
enable_interrupts(global);
osccon = 0x41;
lcd_init();
lcd_send_byte(0,ALL_CLEAR);
while(1){
}
}
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Turns out, send first byte works well.
Then, I tried to send two bytes (which didn't work).
First byte I want to send is 'A' and the second byte is 'B' for simulation.
Master:
| Code: |
#include<16F886.h>
#include<def_16f886.h>
#fuses intrc_io, noprotect
#use delay(clock = 4000000)
#use i2c(master, sda = pin_c4, scl = pin_c3)
void main(void){
osccon = 0x41;
while(1){
delay_ms(1000);
i2c_start();
i2c_write(0xa0);
i2c_write('A');
//i2c_start(); I experimented with this command.
i2c_write('B');
i2c_stop();
}
}
|
Slave:
| Code: |
#include<16f886.h>
#include<def_16f886.h>
#use delay(clock = 4000000)
#include<flex_lcd.h>
#fuses intrc_io, noprotect, debug
#use delay(clock = 4000000)
#use i2c(slave, sda = pin_c4, scl = pin_c3, address = 0xa0)
int8 address = 0;
int8 buffer[5] = {0, 0, 0, 0, 0};
int8 incoming = 0;
int8 first_byte = 0;
int8 second_byte = 0;
int8 state = 0;
#int_ssp
void ssp_interupt ()
{
state = i2c_isr_state();
if(state < 0x80) //Master is sending data
{
incoming = i2c_read(0);
//First received byte is address
if(state==0) first_byte = incoming;
if(state==1) second_byte = incoming;
}
if(state == 0x80) //Master is requesting data
{
i2c_write(buffer[address]);
}
LCD_gotoxy(1,1);
delay_ms(1);
lcd_putc(first_byte);
lcd_putc(second_byte);
}
void main(void){
enable_interrupts(int_ssp);
enable_interrupts(global);
osccon = 0x41;
lcd_init();
lcd_send_byte(0,ALL_CLEAR);
while(1){
}
}
|
Frankly, I have no idea what
| Code: | | state = i2c_isr_state(); |
statement really means (the help file only specifies that for some range, it means the master said read, or the master said write).
Did I do something wrong? or did I miss anything? |
|
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ckielstra
Joined: 18 Mar 2004
Posts: 3680
Location: The Netherlands
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| Re: PIC to PIC communication using i2c |
| Posted: Fri Jul 31, 2009 7:28 am |
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| jk726 wrote: | Frankly, I have no idea what
| Code: | | state = i2c_isr_state(); |
statement really means (the help file only specifies that for some range, it means the master said read, or the master said write). |
The manual is not too bad in this respect, but one piece of information is missing: the returned state value is a 'counter'. For every byte received in this message it will count up until it resets when the next message starts.
| Code: | if(state==0) first_byte = incoming;
if(state==1) second_byte = incoming; |
If you look in the example program ex_slave.c you will see the first byte starts at state==1, not at 0.
Note that this implies a maximum message length of 0x7F bytes (excluding the address). I don't know the I2C specifications well enough to say if this limitation comes from the standard or from CCS. |
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