Nuts and Volts - November 2014

#INT_EXT
 void  EXT_isr(void)
 {
 flags.fremote = 1;
 clear_interrupt(INT_EXT);
 }
#use RS232(baud=9600, xmit=PIN_B7, rcv=PIN_B5,
stream=RADIO)
 
typedef struct{
 unsigned int8 fremote:1;
 }FFLAGS;
FFLAGS flags;
 
unsigned int8 msgON[3];
unsigned int8 msgOFF[4];
unsigned int8 aryIndex;
unsigned int8 nextState;

When the pushbutton is depressed, the fremote flag is set and the external interrupt flag is cleared. It is always best to do as little as possible within the interrupt handler.

The fremote flag will be set within the pushbutton interrupt handler when the pushbutton is depressed.

We will handle the pushbutton physics following the execution of the interrupt handler. Let’s load our message arrays in the initialization function: Normally, a remote control device will send a sequence of binary characters that are decoded at the receiving end.

In this case, I’m going to use human readable messages which will be stored in the arrays msgON and msgOFF.

void init(void)
{
 hw_init();
 output_low(RED_LED); //Both LEDs off
 output_low(GREEN_LED);

Rather than use the mundane i or x as an array index pointer, we will use the aryIndex variable as our array pointer. Our remote control application is very simple and consists of two states (ON and OFF). The nextState variable will determine which state is to be entered with the next pushbutton depression.

msgON[0] = ‘O’;
msgON[1] = ‘N’;
msgON[2] = 0x00;
 
msgOFF[0] = ‘O’;
msgOFF[1] = ‘F’;
msgOFF[2] = ‘F’;
msgOFF[3] = 0x00;

Our pushbutton interrupt handler is to the point:

nextState = 0;
 
flags.fremote = 0;

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