getchar() hanging.

pgaastra · Posted: Thu Oct 28, 2004 8:47 pm

I have a PIC16F84 and run it on a 32kHz watch crystal.
I have compiled the code at the end of this post and connected the pcb to my PC. Using a terminal program I see that the PIC transmits characters correctly but it hangs on the getchar().

I know that the characters are arriving at RB6 (although the PIC is being powered by 3V and the Max 233 levels (with a resistor and zener are a bit high (0-4V)).
Questions: Have I missed out anything obvious.?

Can anybody explain in words the machine code generated by the PCM 2.731 for the getchar() function? I have very little experience in machine code and there seems to be an awful lot of GOTO's.

#include <stdlib.h>
#include "16F84.h"
#fuses LP, NOWDT, NOPROTECT, NOPUT
#USE DELAY(clock = 32760)
#USE RS232(BAUD=300, XMIT = PIN_B7, RCV = PIN_B6)

void main(void){

int character;

set_tris_b(0b01110111); printf("hello world");
while(1){
putchar('a');
while (!kbhit()) ;
character = getchar();
putchar(character);
}
}

asmallri · Joined: 12 Aug 2004 Posts: 1634 Location: Perth, Australia

You are missing the errors keyword from the use RS232 line. If a receive overrun error occurs you will lockup the serial interface. No need for the

Mark · Joined: 07 Sep 2003 Posts: 2838 Location: Atlanta, GA

asmallri · Joined: 12 Aug 2004 Posts: 1634 Location: Perth, Australia

Humberto · Posted: Fri Oct 29, 2004 8:27 am

pgaastra · Posted: Sun Oct 31, 2004 3:34 pm

Thanks for all the ideas.

I changed the baud rate to 110 baud and now the program works.

I only need to send the micro some parameters so 110 baud is OK for now.

pgaastra · Posted: Sun Oct 31, 2004 4:04 pm

I said I changed the baud rate to 110 from 300 and it now works.

I had a look at the machine code produced by the compiler for each baud rate, for getchar() and it's identical. How can that be? I thought the software uart would look for an edge of the start bit and then look at the RX pin at the mid point of the subsequent bits. If the code is identical, how can the timing be right for both baud rates?