Problem in a code for PIC16F84 to act as a data converter

[cwt]

registers counting wrong pic16f84

Hi there..
Currently, i am trying on the PIC16F84 to act as a serial to parallel data converter..
I'll enclose my source code here..
There a problem surface when i try my code.
The 8LEDs (represent 8 parallel bits) will not light up accordingly. Sometimes will get the right output, sometimes wont. Most of the time, it is the wrong output.


LIST p=16F84
include "P16F84.inc"

;------------------------------------------------------------------

CBLOCK 0x20 ;starting address of general register

BIT_COUNTER
NEXT_BIT
DELAY_COUNT
TEMP_STORE

ENDC

;------------------------------------------------------------------

BSF STATUS, RP0 ;initialize RA0 as input
MOVLW 0x01
MOVWF TRISA
BCF STATUS, RP0
CLRF PORTA

BSF STATUS, RP0 ;initialise portB as output
MOVLW 0x00
MOVWF TRISB
BCF STATUS, RP0
CLRF PORTB

GOTO START ;go to main program

;------------------------------------------------------------------


START_DELAY MOVLW 0x0C ;subroutine to delay 52us
MOVWF DELAY_COUNT
START_WAIT NOP
DECFSZ DELAY_COUNT, 1
GOTO START_WAIT
RETURN

;-------------------------------------------------------------------

BIT_DELAY MOVLW 0x18 ;subroutine to delay 104us
MOVWF DELAY_COUNT
BIT_WAIT NOP
DECFSZ DELAY_COUNT, 1
GOTO BIT_WAIT
RETURN

;-------------------------------------------------------------------

START BTFSC PORTA, 0 ;detect start bit
GOTO START
CALL START_DELAY ;make sure start bit is still there
BTFSC PORTA, 0
GOTO START

MAIN CLRF PORTB

CALL BIT_DELAY
BTFSC PORTA, 0
BSF TEMP_STORE, 0

CALL BIT_DELAY
BTFSC PORTA, 0
BSF TEMP_STORE, 1

CALL BIT_DELAY
BTFSC PORTA, 0
BSF TEMP_STORE, 2

CALL BIT_DELAY
BTFSC PORTA, 0
BSF TEMP_STORE, 3

CALL BIT_DELAY
BTFSC PORTA, 0
BSF TEMP_STORE, 4

CALL BIT_DELAY
BTFSC PORTA, 0
BSF TEMP_STORE, 5

CALL BIT_DELAY
BTFSC PORTA, 0
BSF TEMP_STORE, 6

CALL BIT_DELAY
BTFSC PORTA, 0
BSF TEMP_STORE, 7

CALL BIT_DELAY
MOVF TEMP_STORE, 0
MOVWF PORTB

GOTO START

END

 

[cwt]

pic16f84 rs232 9600 bps

I am using 9600 bps and 4Mhz crystal oscillator.

 

[tgq]

Re: PIC16F84

Sometimes will get the right output, sometimes wont. Most of the time, it is the wrong output.

yes you must re-synchronize
but if you want to build a real RS232 to parallel interface the best way is to change PIC with built-in USART, data flow control lines and program a data buffer

 

[cwt]

PIC16F84

re-synchronize means?i have to alter the delay time?

 

[checkmate]

Re: PIC16F84

I got 51us and 99us (excluding CALL instruction) for your 2 delay routines on a rough count. Kindly check them again.

 

[C-Man]

Re: PIC16F84

What does your input circuit for RS232 look like?

MAX232 or transistor or direct connection?

How are your configuration fuses for the 16C84?

best regards

 

[cwt]

PIC16F84

i am using max232.
my delay routine is wrong?

 

[C-Man]

Re: PIC16F84

Your delay routines should be OK, it does not really matter if you delay for 49 or 51 (or 102 instead of 104) uS

But I would check Temp_Store as you forget to clear it after you have received 8 databits ...

CALL BIT_DELAY
MOVF TEMP_STORE, 0
MOVWF PORTB
CLRF TEMP_STORE ;<-- insert this here

GOTO START


best regards