Hi All,

I had a test program running which received and echoed back character from a
PC serial port connected to the USART of a PIC 16F877. The code worked, and
in fact is the sample at piclist.com by Claudio Rachiele. It can be found at
http://www.piclist.com/techref/microchip/16F877/rs232-cr.htm

The problem is that the code broke when I add a simple subroutine. The
subroutine writes to PORTC and I suspect this might cause the problem.
Basically, if I call the subroutine before the serial receive and transmit
subroutines, the transmit subroutine goes into an infinite loop while
checking the TXIF bit. The exact location the subroutine is called from in
the code linked above is just before the "baud rate settings" comment. Below
is the subroutine, I8255WriteConfigRegister, are there any obvious errors?
Thanks in advance.

Lindsay

I8255WriteConfigRegister
; set address lines of the 8255 to access its config register
 movlw b'00001111'
 movwf PORTC
; load the config value and write it to the config register
 movf I8255CONFIGVALUE, W
 movwf    PORTD   ; load the config byte onto the data lines
 call I8255WriteStrobe  ; write the config byte
 return

I8255WriteStrobe
; change pic PORTD pins into output
 banksel TRISA
 movlw b'00000000'
 movwf TRISD
 banksel PORTA

 bcf PORTC, I8255CONTROL_WRITE
 call Delay200ns
 bsf PORTC, I8255CONTROL_WRITE
 call Delay200ns  ; to meet minimum delay req. between WR and RD
 return

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