Simple RS232 interrupt routine

[mkr]

Good Morning All,
I am trying to dabble a simple RS232 routine. I am sending a byte 0x68 from PC, I read this byte and send back the same byte to the PC.

The problem is I am recieving the byte so the RDA interrupt is working, but some how I am finding it diffcult to transmit this byte back to PC. I have a simple COM port monitoring app. running on the PC.

Here is the code I am working on, could some body help me out, whats wrong. The direction pin is PIN_J4.

//this is the header file

#include <18F8722.h>
#device ICD=TRUE
#device adc=8
#use delay(clock=16000000)
#fuses NOWDT,WDT128,HS, NOPROTECT, IESO, BROWNOUT, BORV25, NOPUT, NOCPD, STVREN, NODEBUG, LVP, NOWRT, NOCPB, NOEBTRB, NOEBTR, NOWRTD, NOWRTC, NOWRTB, FCMEN, LPT1OSC, MCLR, XINST, MCU
#use rs232(baud=19200,parity=N,xmit=PIN_C6,rcv=PIN_C7,bits=8,stream = COM1)

char c=0;
char senddata=0;
int8 count=0;
void send(char c);

// end of header file

//start of interrupt and main

#int_RDA
RDA_isr()
{
c = fgetc(COM1);
output_high(PIN_J4);
}

#int_TBE
TBE_isr()
{
fputc(c, COM1);
}

void main()
{

setup_adc_ports(NO_ANALOGS|VSS_VDD);
setup_adc(ADC_OFF|ADC_TAD_MUL_0);
setup_psp(PSP_DISABLED);
setup_spi(FALSE);
setup_wdt(WDT_OFF);
setup_timer_0(RTCC_INTERNAL);
// setup_timer_1(T1_INTERNAL|T1_DIV_BY_4);
setup_timer_1(T1_DISABLED);
setup_timer_2(T2_DISABLED,0,1);
setup_timer_3(T3_DISABLED|T3_DIV_BY_1);
setup_timer_4(T4_DISABLED,0,1);
setup_comparator(NC_NC_NC_NC);
setup_vref(FALSE);
// enable_interrupts(INT_TIMER1);


enable_interrupts(INT_RDA);
enable_interrupts(INT_TBE);
disable_interrupts(INT_TBE);
enable_interrupts(GLOBAL);

for(;;){
if(c==0x68){
send(c);
}
}

}

void send(char c){
senddata = c;
output_low(PIN_J4);
enable_interrupts(INT_TBE);
}

// program end
_________________
Thanks

mkr

[Ttelmah]

You can't use TBE, the way you are trying to do it. The problem is that TBE, will continuously occur, when the transmit is 'empty'.
Start with TBE _disabled_ in the main code. Then with just the single byte, use:

[mkr]

Thanks for the reply. I still cannot get it working. I am not using tx interrupt, and trying to rx byte and send the same byte back from the rx interupt routine. I dont know where i am going wrong.

What should I do with the direction pin. Should I make it high, when recieving byte and make the pin low when transmitting byte. Is this right...

here is the sample code...
#int_RDA
RDA_isr()
{
c = fgetc(COM1);
// output_high(PIN_J4);
enable_interrupts(INT_TBE);

// output_low(PIN_J4);
fputc(c,COM1);
disable_interrupts(INT_TBE);
}
/*
#int_TBE
TBE_isr()
{
fputc(senddata, COM1);
disable_interrupts(INT_TBE);
}
*/

Could somebody show an simple interrupt routine with recieving and transmitting data.
_________________
Thanks

mkr

[PCM programmer]

There are no nested interrupts allowed. They are not supported.
That's why your code doesn't work. You're hoping that a TBE interrupt
will occur in the middle of processing the RDA isr. But it can't.

I need to modify the comment above. It's true for your code, as posted.
But for the 18F series you can do a high priority interrupt. See this
thread.
http://www.ccsinfo.com/forum/viewtopic.php?t=26085
But I don't think you need to do it in your test program.

[rnielsen]

Do not use the TBE_isr. An interrupt, for the TBE_isr will happen when the Transmit buffer is Empty. So, if you're not transmitting, the buffer will be empty. Therefore, an interrupt will be created and the TBE_isr will be entered. Now, since you're not transmitting anything, again, it will create an interrupt and enter the ISR again. This will hog ALL of your CPU time and nothing will get done.

Simply enable the RDA interrupt and put your fgetc() inside it and then have a fputc() right after it. This will, in effect, echo whatever character the serial port receives.

[Ttelmah]

The problem is that the 'point'of using interrupts, is to allow the communication to be asynchronous to the main program flow. As such serial interrupt routines, won't be designed to handle single characters, but will be buffered I/O routines, and will be more complex than you seem to be looking for. Your original code would work as shown here.

[mkr]

I have two rs232 ports to be serviced. The first one using the 1st internal interrupt rda/tbe and the second using internal interrupt rda2/tbe2. The first interrupt has to be serviced as fast as possible then the second interrupt. Do I need to set priority for these interrupts to be serviced. If so how to do it.

I found the previous reply very usefull, but where could I find an article or write up of interrupt handling using CCS or for any micro controller application. I read many books but but nothing seems to help with an practical approach in implementing the interrupt handlers.

Your suggestion appreicated.
_________________
Thanks

mkr

[Ttelmah]

First, interrupts are serviced when they occur, with the global handler, checking the interrupts in the order they are defined (or in the order set in the #priority statement, if one is present). On chips with dual UARTs (which will be 18F chips), it is possible to have one serial using the high priority interrupt, but this will probably bring more complexity than it possibly warrants (it depends on what other interrupts are being used).
So, unless the two UART's interrupt nearly simultaneously (relatively unlikely for asynchronous events), whichever interrupts first, will normally be serviced first. Remember that you always hve at least a whole character time to service the interrupt, so normally, unless the rates are very high, pioritisation becomes uneccessary.
Now you give no idea about the data rates involved, but I'll attach a modified set of 'generic'

interrupt driven set of RS232 handlers, which should give a start.