Motor Control

[Wura]

I am using the PIC 16F874, I am trying to change the direction of a DC motor by simple interupt switches. I am outputing to an L272 chip which drives the motor and accepts two logic inputs. A C0 of one and C1 of zero puts a postivive voltage on the motor and a C0 of zero and C1 one should but a negative voltage on my motor. The L272 chip works fine independently of the PIC and the PIC works fine without connecting to the L272 chip. When I hook them together I can only get the motor to run in one direction.

Please can you take a look at my code and see if i am doing something wrong.

#include <16F874.H>
#use delay(clock=20000000)
char event;

void main()
{
enable_interrupts(INT_rb);
enable_interrupts(global);


// Initializing default values
event = 'r';


while(event == 'r')
{
//motor forward
output_low(PIN_C1);
output_high(PIN_C0);

}

while(event == 'g')
{
output_high(PIN_C1);
output_low(PIN_C0);
}
}


#int_rb
rb_isr ( )

{

// Initializing everything
byte changes;
int last_b;
int port_b;
changes = last_b ^ port_b;
last_b = port_b;

// if wheel has went one complete revolution
if (!input(PIN_b7)){event = 'r';}

// if bob hit grain
if (!input(PIN_b6)){event = 'g';}

// if bob is at housing
if (!input(PIN_b5)){event = 'h';}

//debounce
delay_ms(100);

}

[SherpaDoug]

What direction does the motor spin in? What are the logic lines doing when the motor is spinning the wrong way? Can you put a meter, or better yet a scope on them? Is the motor putting noise on the PIC power line?
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[Ttelmah]

The first few lines of the interrupt handler do nothing. You need to declare 'last_b', as a _static_ variable, or it's contents may be lost between interrupts. Also the code looks as if it was an attempt to see the port bit changes (in which case, 'port_b', wants to actually be the 'port', rather than a normal variable. As a second general comment _get rid of the delay in the interrupt handler_...
I'd suspect the code actuall wants to be: