Hi all.
I'm tearing my hair out here at the moment trying to get a serial line
to work with a 16c74a. It will transmit perfectly fine, but when I try
to recieve a character, store it, retrieve it and send it back, the chip
barfs - literally. I get wierd output on the serial line and then the
chip stops and has to be reset.
I've tagged the code on below here - does anyone see something I've
missed ?
Tearing my hair out ...

 ERRORLEVEL 0
 TITLE  "Serial Line Test Program"
 SUBTITLE "Initial polled version"
 LIST p=16c74a, b=4, n=85
 PAGE

;  Serial line test program
;

#include "p16c74a.inc"

#define ClkFreq  20000000
#define baudrate D'32'  ;9600 Baud (from p102, datasheet)
#define TXSTA_INIT 0xA0
#define RCSTA_INIT 0x90

RX   equ  H'0021'  ;Stores data recieved

; PIC Configuration word
 __config _CP_OFF&_BODEN_OFF&_WDT_OFF&_HS_OSC


 org 0000

RESET goto Start

 org 0005

Start call Initialise_LED
  call Setup_Async_Mode
  movlw A'-' ;initial character
  movwf RX

  goto Serial_Data_Poll_Loop

 org 0100

Setup_Async_Mode
   bcf  STATUS,RP1
   bsf  STATUS,RP0

   movlw baudrate
   movwf SPBRG

   bcf  TRISC,7
   bsf  TRISC,6

   movlw TXSTA_INIT
   movwf TXSTA

   bcf  STATUS,RP0

   movlw RCSTA_INIT
   movwf RCSTA
   return

Serial_Data_Poll_Loop

PollTx  btfss PIR1,TXIF  ;ready to transmit ?
   goto PollTx
   movf RX,0  ;Load Data
   movwf TXREG  ;Transmit data

PollRx  btfss PIR1,RCIF  ;Data recieved ?
   goto  PollRx
   movf  RCREG,0  ;Load data into W
   movwf RX
   goto Serial_Data_Poll_Loop ;Reloop
 END

--
Mark Dennehy, B.A., B.A.I.  Email : mdennehy@tcd.ie
Research Student,
Computer Vision and Robotics Research Group,
Computer Science Dept., Trinity College Dublin