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USART serial comms on 16f688 problems

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I'm using the 16F688 pic, I've got it to flash an led on and off, wait for a button to be pressed before running some code, but I haven't been able to get it to talk to my PC yet. My code is attached, can anyone see anything obviously wrong with it - it's probably something simple I'm forgetting. Also I'm using the PicKit1 kit with the serial part populated with a max 232 etc, if that helps.

Thanks

Code:
;**********************************************************************
;   This file is a basic code template for object module code         *
;   generation on the PICmicro PIC16F688. This file contains the      *
;   basic code building blocks to build upon.  As a project minimum   *
;   the 16F688.lkr file will also be required for this file to        *
;   correctly build. The .lkr files are located in the MPLAB          *
;   directory.                                                        *
;                                                                     *
;   If interrupts are not used all code presented between the         *
;   code section "INT_VECTOR and code section "MAIN" can be removed.  *
;   In addition the variable assignments for 'w_temp' and             *
;   'status_temp' can be removed.                                     *
;                                                                     *
;   If interrupts are used, as in this template file, the 16F688.lkr  *
;   file will need to be modified as follows: Remove the lines        *
;     CODEPAGE   NAME=vectors  START=0x0      END=0x4      PROTECTED  *
;   and                                                               *
;     SECTION    NAME=STARTUP  ROM=vectors                            *
;   and change the start address of the page0 section from 0x5 to 0x0 *
;                                                                     *
;   Refer to the MPASM User's Guide for additional information on     *
;   features of the assembler and linker (Document DS33014).          *
;                                                                     *
;   Refer to the respective PICmicro data sheet for additional        *
;   information on the instruction set.                               *
;                                                                     *
;**********************************************************************
;                                                                     *
;    Filename: Flashing LED1.asm                                      *
;    Date: 2009/04/20                                                 *
;    File Version: 1.0                                                *
;                                                                     *
;    Author: Jules Lewarne                                            *
;    Company:                                                         *
;                                                                     *
;                                                                     *
;**********************************************************************
;                                                                     *
;    Files required:                                                  *
;                    16F688.lkr                                       *
;                                                                     *
;                                                                     *
;**********************************************************************
;                                                                     *
;    Notes:                                                           *
;                                                                     *
;                                                                     *
;                                                                     *
;                                                                     *
;**********************************************************************

	list      p=16F688           	; list directive to define processor
	#include <p16F688.inc>        	; processor specific variable definitions

	errorlevel  -302              	; suppress message 302 from list file

; '__CONFIG' directive is used to embed configuration word within .asm file.
; The lables following the directive are located in the respective .inc file.
; See data sheet for additional information on configuration word settings.

	__CONFIG    _CP_OFF & _CPD_OFF & _BOD_OFF & _PWRTE_ON & _WDT_OFF & _INTRC_OSC_NOCLKOUT & _MCLRE_OFF & _FCMEN_OFF & _IESO_OFF



;***** VARIABLE DEFINITIONS 

; FORMAT: [name]	RES	[number of bytes reserved]
INT_VAR		UDATA_SHR	0x71   
DVAR	RES 1
DVAR2	RES 1
DVAR3	RES 1

;**********************************************************************
RESET_VECTOR	CODE	0x000		; processor reset vector
		goto    Main            ; go to beginning of program


INT_VECTOR	CODE	0x004		; interrupt vector location
		retfie                  ; return from interrupt

;**********************************************************************
;	Function Name: MAIN
;	
;	Parameters:
;
;	Description: This is the main program which is executed once the processor
;		has powered up.
;		The code within this routine performs some device initialisation then
;		flashes an LED. This routine makes use of another routine which causes
;		a short delay by sending the prcessor into a loop which decrements from
;		an arbitrary value until it reaches zero.
;**********************************************************************

Main
		
		;		
		
		
		;Device Initialisation
		
        bsf     STATUS,RP0  ; set file register bank to 1
        clrf    ANSEL       ; switch off analog-to-digital conversation system (analog inputs : off) 
        
        movlw   B'11001111' ; Set Ports to I/O, TRISA register: [X][X][RA5][RA4][RA3][RA2][RA1][RA0]
        movwf   TRISA    	;									Don't  I/O	I/O	  I	  I/O  I/O  I/O
							;									Care    
							
		
        bcf     STATUS,RP0  ; set file register bank to 0

        movlw   B'00000111' ; switch off the comparator, enable digital i/o
        movwf   CMCON0      ;
		clrf	ADCON0		; switch off ADC module
		bcf		PORTA, 5
		
		clrf PORTA ; Set all PORTA outputs to zero
		bsf		TXSTA,5
		bcf		TXSTA,4
		bsf		TXSTA,2
		bsf		RCSTA,7
		bcf		BAUDCTL,3
		movlw	B'00011001' ; setup baudrate generator
		movwf	SPBRG

Loop  
		;btfsc PORTA,3 ; Wait for button on RA3
        ;goto Loop

				; PORTA register: [X][X][RA5][RA4][RA3][RA2][RA1][RA0]
     			;				   Don't  I/O	I/O	  I	  I/O  I/O  I/O
				;				   Care    
				;						   D0/D1   D2/D3  D6/D7
				;						  o-!>!-o---!>!--o-!>!-o
				;						  o-!<!-o---!<!--o-!<!-o
				;							   D4/D5
				;						  o-----!>!------o
				;						  o-----!<!------o


		;movlw B'00010000' ; PORTA Register
		;movwf PORTA

	
		bsf 	PORTA,4
		call 	Delay
		bcf 	PORTA,4 ; set BIT 4 of PORTA to zero
		call 	Delay
		
		movlw	B'01000001' ; = 'A' in ASCII
		movwf	TXREG
		
		
		
Goto Loop
;**********************************************************************************
Delay
    	movlw		0xff	; set outer delay loop (change these hex number to change the frequency)
    	movwf		DVAR2	; memory location
Delay0
    	movlw		0xff	; set inner delay loop  (change these hex number to change the frequency)
    	movwf		DVAR	; incremental memory
 							; location
Delay1	decfsz		DVAR,1
		goto		Delay1
    	decfsz		DVAR2,1
    	goto		Delay0
		
    	return



; initialize eeprom locations

EE		CODE	0x2100
		DE	0x00, 0x01, 0x02, 0x03


		END                       ; directive 'end of program'
 
Last edited:

Pommie

Well-Known Member
Most Helpful Member
You appear to have it setup for 2400 baud but it is quite hard to follow the rest of the code as you have used numbers.

Can I suggest you change things like,
Code:
	bcf	BAUDCTL,3
To,
Code:
	bcf	BAUDCTL,BRG16
This will make it easier to work out what you are doing.

Mike.
 

mister_e

New Member
From what I see, the actual setup should be for 9600 bauds @4MHz.

Looks like an hardware problem to me, I would suggest to scope your signal, at the PIC output, then at your MAX232 output.
 
Working now, changed the numbers to named parameter - much easier to see what's going on. The problem was in the hardware, tx and rx were reversed, just that simple! Thanks
 
Last edited:
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