UART test program for 16F628

Function
This program sends an alive message and then echoes characters received from a terminal via RS232.

Hardware
The testboard K4 is set up with reset circuit and a MAX232 for RS232 communication. The 4 capacitors connected to MAX232 are 1 uF types; if you use MAX232A or ST232, they can be 100 nF values. The 4 arrows in the circuit diagram indicate signal direction.


Testboard K4 configured for 628uart.asm

Software in assembler
;*******************************************************************
; Function:  Sends alive message, then echoes characters at 9600 bps
; Processor: PIC16F628 at 4 MHz using internal RC oscillator
; Hardware:  Testboard K4
; Filename:  628uart.asm
; Author:    Lars Petersen, oz1bxm@pobox.com
; Website:   www.qsl.net/oz1bxm/PIC/pic.htm
; Credit:    Tony Nixon's test program at
;            www.piclist.com/techref/microchip/16f877/setup.htm
;*******************************************************************

        LIST P=16F628, R=DEC    ; Use the PIC16F628 and decimal system

        #include "P16F628.INC"  ; Include header file

        __config  _INTRC_OSC_NOCLKOUT & _LVP_OFF & _WDT_OFF & _PWRTE_ON & _BODEN_ON

        CBLOCK 0x20             ; Declare variable addresses starting at 0x20
          dataL
        ENDC

        ORG    0x000            ; Program starts at 0x000
;
; --------------------------------
; SET ANALOG/DIGITAL INPUTS PORT A
; --------------------------------
;
        movlw 7
        movwf CMCON             ; CMCON=7 set comperators off
;
; ----------------
; INITIALIZE PORTS
; ----------------
;
        movlw b'00000000'       ; set up portA
        movwf PORTA

        movlw b'00000100'       ; RB2(TX)=1 others are 0
        movwf PORTB

        bsf STATUS,RP0          ; RAM PAGE 1

        movlw 0xFF
        movwf TRISA             ; portA all pins input

        movlw b'11110010'       ; RB7-RB4 and RB1(RX)=input, others output
        movwf TRISB

; ------------------------------------
; SET BAUD RATE TO COMMUNICATE WITH PC
; ------------------------------------
; Boot Baud Rate = 9600, No Parity, 1 Stop Bit
;
        movlw 0x19              ; 0x19=9600 bps (0x0C=19200 bps)
        movwf SPBRG
        movlw b'00100100'       ; brgh = high (2)
        movwf TXSTA             ; enable Async Transmission, set brgh

        bcf STATUS,RP0          ; RAM PAGE 0

        movlw b'10010000'       ; enable Async Reception
        movwf RCSTA
;
; ------------------------------------
; PROVIDE A SETTLING TIME FOR START UP
; ------------------------------------
;
        clrf dataL
settle  decfsz dataL,F
        goto settle

        movf RCREG,W
        movf RCREG,W
        movf RCREG,W            ; flush receive buffer
;
; ---------
; MAIN LOOP
; ---------
;
        call message            ; send "16F628 alive"
loop    call receive            ; wait for a char
        call send               ; send the char
        goto loop
;
; -------------------------------------------
; RECEIVE CHARACTER FROM RS232 AND STORE IN W
; -------------------------------------------
; This routine does not return until a character is received.
;
receive btfss PIR1,RCIF         ; (5) check for received data
        goto receive

        movf RCREG,W            ; save received data in W
        return
;
; -------------------------------------------------------------
; SEND CHARACTER IN W VIA RS232 AND WAIT UNTIL FINISHED SENDING
; -------------------------------------------------------------
;
send    movwf TXREG             ; send data in W

TransWt bsf STATUS,RP0          ; RAM PAGE 1
WtHere  btfss TXSTA,TRMT        ; (1) transmission is complete if hi
        goto WtHere

        bcf STATUS,RP0          ; RAM PAGE 0
        return
;
; -------
; MESSAGE
; -------
;
message movlw  '1'
        call send
        movlw  '6'
        call send
        movlw  'F'
        call send
        movlw  '6'
        call send
        movlw  '2'
        call send
        movlw  '8'
        call send
        movlw  ' '
        call send
        movlw  'a'
        call send
        movlw  'l'
        call send
        movlw  'i'
        call send
        movlw  'v'
        call send
        movlw  'e'
        call send
        movlw  0x0D ; CR
        call send
        movlw  0x0A ; LF
        call send
        return

        END
Remarks
The ST232 is used for RS232 communication. An MAX232 can also be used. A simpler circuit can be set up using DS275, see the homepage of Wichit Sirichote from Thailand.
A terminal program (HyperTerminal) is set up for 9600 baud with 8 data bits, no parity, no flowcontrol and 1 stop bit.


Port settings in HyperTerminal


The alive message displayed in HyperTerminal

The same program written in C is here.

Download
Download 628art.zip containing the source code in assembler and the hexfile.

Trouble shooting
You might find this trouble shooting page useful: PIC16F628 UART trouble shooting

Credit
Tony Nixon's UART test program at http://www.piclist.com/techref/microchip/16f877/setup.htm was my source for the above program. Thanks!

Example application
Hein Ragas shows on his webpage Buffered USART communications how the UART test program is used as a part of a more advanced application (morse code flasher with 16 byte circular buffer).



This page created 14-Oct-2002 by Lars Petersen, oz1bxm@pobox.com
Latest update 14-Oct-2009.

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