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elb0m
Joined: 20 Jan 2011
Posts: 3
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| I2C Master - Slave problem |
 Posted: Thu Jan 20, 2011 8:14 am |
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Hello.
I want to connect 2 PIC16F876A motors with I2C protocol.
On the breadboard I have 2 resistors 2.2 Kohms, one IC by Philips called PCF8574, 4 Yellow LEDS and the 2 PICS.
I have setup one as a master and the other one as a slave.
Also the IC is slave with address 0x40.
MASTER CODE:
| Code: |
#include <16f876A.H>
#device adc=8
#fuses HS, NOWDT, NOBROWNOUT, NOPROTECT, PUT, NOLVP
#use delay(clock=40000000)
#use i2c(Master, sda=PIN_C4, scl=PIN_C3)
#define SLAVE1_WRT_ADDR 0x40
#define BUF_SIZE 8
//====================================
int trans;
void main()
{
trans=0;
while(1){
trans = trans + 1;
delay_ms(300);
i2c_start();
i2c_write(SLAVE1_WRT_ADDR);
i2c_write(trans);
i2c_stop();
delay_ms(300);
i2c_start();
i2c_write(0xA0);
i2c_write(trans);
i2c_stop();
}
}
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SLAVE
| Code: |
#include <16F876A.H>
#device adc=8
#fuses HS, NOWDT, NOBROWNOUT, NOPROTECT, PUT, NOLVP
#use delay(clock=4000000)
BYTE address, buffer[0x10];
#include <lib_mot_moway.h>
void motor_move_for();
void motor_move_back();
#INT_SSP
void ssp_interupt ()
{
BYTE incoming, state;
state = i2c_isr_state(TB);
if(state <= 0x80) //Master is sending data
{
incoming = i2c_read(TB);
if(state == 1) //First received byte is address
{address = incoming;
motor_move_for();}
if(state == 2){
motor_move_back();
buffer[address] = incoming;}
}
if(state == 0x80) //Master is requesting data
{
i2c_write(TB,buffer[address]);
}
}
void main ()
{
enable_interrupts(GLOBAL);
enable_interrupts(INT_SSP);
while (TRUE) {}
}
void motor_move_for()
{
MOT_STR(30, FWD, TIME, 10);
while(!input(MOT_END)){}
}
void motor_move_back(){
MOT_STR(30, BACK, TIME, 10);
while(!input(MOT_END)){}
}
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The leds connected on the PCF 8574, light on like a charm(count right) but the slave PIC has a problem. It doesn't get interrupted at once. It gets after several times (if it does) and only executes the routine move_motor_forward.
I have no clue why this is happening. Thanks.
edit
_
Even without the part where I send to pcf I still have the same problem.
_________________
sins can't be undone |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19509
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| Posted: Thu Jan 20, 2011 9:09 am |
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You don't appear to have a #use I2C, telling the slave that it's address is 0x40....
Take the movement commands out of the I2C handler. Set a flag, to say move forwards/back, and have the main code do this. Problem here is that your movements could last 'for ever', and the I2C slave receive code is _hung_ while this is happening. The bus is effectively 'jammed'....
Old 'mantra' repeated here many times. In an interrupt handler _handle_ the hardware event, and get out again ASAP. This is _essential_....
Best Wishes |
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elb0m
Joined: 20 Jan 2011
Posts: 3
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| Posted: Thu Jan 20, 2011 10:12 am |
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The use #i2c is included in the .h file that I have.
So I must set a flag, in the int_ssp and in the main program check the flag?
Ok I will do that as soon as I get back home!
Didn't understand what you said about that old mantra:/
And on that interrupt handler you mean the int_ssp right?
_________________
sins can't be undone |
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elb0m
Joined: 20 Jan 2011
Posts: 3
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| Posted: Fri Jan 21, 2011 6:37 am |
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OK.
I've changed the code as you told me.
Some problems occur though.
Here is the code.
MASTER
| Code: |
#include <16f876A.H>
#device adc=8
#fuses HS, NOWDT, NOBROWNOUT, NOPROTECT, PUT, NOLVP
#use delay(clock=40000000)
#use i2c(Master, sda=PIN_C4, scl=PIN_C3)
#define SLAVE1_WRT_ADDR 0x40
#define BUF_SIZE 8
//====================================
void main()
{
i2c_start();
i2c_write(0xA0);
i2c_write(0x13);
i2c_stop();
}
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SLAVE
| Code: |
#include <16F876A.H>
#device adc=8
#fuses HS, NOWDT, NOBROWNOUT, NOPROTECT, PUT, NOLVP
#use delay(clock=4000000)
BYTE address,data, buffer[0x10];
#use i2c(SLAVE, SDA=PIN_C4, SCL=PIN_C3, address=0xA0,stream=TB)
#include <lib_sen_moway.h>
int flag;
#INT_SSP
void ssp_interupt ()
{
BYTE incoming, state;
state = i2c_isr_state(TB);
if(state <= 0x80) //Master is sending data
{
incoming = i2c_read(TB);
if(state == 1) //First received byte is address
{
flag = 1;
address = incoming;
}
if(state == 2){
flag = 2;
data = incoming;}
}
if(state == 0x80) //Master is requesting data
{
i2c_write(TB,buffer[address]);
}
}
void main ()
{ flag =0;
enable_interrupts(GLOBAL);
enable_interrupts(INT_SSP);
while (TRUE) {
if (flag==1){ LED_R_ON(); }
if (flag==2){ LED_L_ON(); if (data==0x13){LED_TOP_GREEN_ON();} }
}
}
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So, i have both processors OFF.
I turn the slave ON(while(TRUE) loop waits for the flag, and the interrupt).
then
I turn the master ON.
Results:
Sometimes on the first time i turn the master ON the LED Right(LED_R_ON) turns on. I may have to turn several times master on-off-on-off to get that LED Right on. It doesn't get INTERRUPTED at once. When i have in while loop it works(LED_R_ON).
I don't see thought the LED_L to be turning on,neither the TOP_GREEN.
I can't understand the problem.
It might be the voltage, the resistors?
2.8V and 2.2K Resistors.
Thanks
_________________
sins can't be undone |
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Ttelmah
Joined: 11 Mar 2010
Posts: 19509
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| Posted: Fri Jan 21, 2011 10:55 am |
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First, what powers the pull-ups?.
If it is the master, then the slave _needs_ to wait for the lines to go high, before enabling the bus. So something like:
| Code: |
while ( (input(PIN_C4)==0 || input(PIN_C3)==0) ;
//Now start the interrupt
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Otherwise it could easily see the bus as in an indeterminate start/stop condition, and get into a hung state, before starting.....
2.2K, is 'highish', if your bus really is at 2.8v. Depends on your likely bus capacitance, but for 2.8v, the minimum value for the pull-ups, is just 800R. I'd suggest something like 1.2K, would be safer at such a low voltage.
When the 876A, was designed, the _minimum_ specified voltage for I2C, was 3V (it has since been reduced), and I'd be significantly worried whether this chip is actually going to be happy running I2C at such a low voltage...
Best Wishes |
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