RS-232 with 16F877 - Electronic Circuits Projects Diagrams Free

MikeyG79 · 12th April 2004, 03:09 PM

Starting out a new project and just trying to write some bits for my computer to read (just using cat /dev/ttyS1)- here is part of what I have so far, not sure why it doesn't work

Main:
call Print_Message
movlw 90H
movf TXREG
call Delay1sec
goto Main

Print_Message:
call LCD_Init
call Delay10ms

movlw MSG1
;movwf TXREG
call LCD_PrintString
call LCD_NewLine
movlw MSG2
call LCD_PrintString

call Delay1sec

call LCD_Init
call Delay10ms
movlw MSG3
call LCD_PrintString
call LCD_NewLine
;call Voltage
movlw MSG4
call LCD_PrintString
call Delay1sec
return

Exo · 12th April 2004, 03:12 PM

Do you setup the uart somewhere else in your code?. The pic's uart requires some setup code before you can start copying things to TXREG
Secondly, you should check bit TXIF of register PIR1 to see you are allowed to write new data to TXREG. This flag indicates the usart is ready for transmission.

MikeyG79 · 12th April 2004, 03:16 PM

Ooops, guess I missed copying some code-

LIST p=16F877
#include "p16f877.inc"
errorlevel 1, -302 ;Suppress bank 0 messages

; Memory Declarations
cblock 0x20 ; Start of general purpose memory
endc

ORG 0x000
Start:
goto Init ; Execute code

ORG 0x004
Interrupt:
goto Init ; Ignore interrupts

Init:
BANKSEL TRISA
movlw b'11111111'
movwf TRISA

BANKSEL TRISB
movlw b'11111111' ; All inputs including user buttons
movwf TRISB

BANKSEL TRISC
movlw b'11110000' ; LED lines as outputs
movwf TRISC

BANKSEL TRISD
movlw b'00000000' ; LCD lines all are outputs
movwf TRISD

BANKSEL OPTION_REG
movlw b'00000111' ; 0=PortB weak<7>,(Intedg<6>),(T0CS<5>),(T0SE<4>),(PSA<3>)25 6<210>
movwf OPTION_REG

;;;; Initialize UART
BANKSEL SPBRG
; Set up baud rate (9600)
movlw .129
movwf SPBRG
; Set up serial port
movlw 0x24
movwf TXSTA
BANKSEL RCSTA
; Enable port
movlw 0x90
movwf RCSTA

BANKSEL PORTA ; Normal bank again

Exo · 12th April 2004, 03:25 PM

Can't see anything wrong with the setup code at first glance

But you'll need to check TXIF before transmitting

Code:

Transmits W over the serial port

SerialTransmit
		
	   BANKSEL TXREG
		BTFSS	PIR1, TXIF		;Buffer empty?
		GOTO 	$-1				;no? then wait until it is
		MOVWF	TXREG			;Transmit W
		RETURN

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12th April 2004, 03:09 PM	#1
MikeyG79	RS-232 with 16F877 Starting out a new project and just trying to write some bits for my computer to read (just using cat /dev/ttyS1)- here is part of what I have so far, not sure why it doesn't work Main: call Print_Message movlw 90H movf TXREG call Delay1sec goto Main Print_Message: call LCD_Init call Delay10ms movlw MSG1 ;movwf TXREG call LCD_PrintString call LCD_NewLine movlw MSG2 call LCD_PrintString call Delay1sec call LCD_Init call Delay10ms movlw MSG3 call LCD_PrintString call LCD_NewLine ;call Voltage movlw MSG4 call LCD_PrintString call Delay1sec return

12th April 2004, 03:12 PM	#2
Exo	Do you setup the uart somewhere else in your code?. The pic's uart requires some setup code before you can start copying things to TXREG Secondly, you should check bit TXIF of register PIR1 to see you are allowed to write new data to TXREG. This flag indicates the usart is ready for transmission.

12th April 2004, 03:16 PM	#3
MikeyG79	Ooops, guess I missed copying some code- LIST p=16F877 #include "p16f877.inc" errorlevel 1, -302 ;Suppress bank 0 messages ; Memory Declarations cblock 0x20 ; Start of general purpose memory endc ORG 0x000 Start: goto Init ; Execute code ORG 0x004 Interrupt: goto Init ; Ignore interrupts Init: BANKSEL TRISA movlw b'11111111' movwf TRISA BANKSEL TRISB movlw b'11111111' ; All inputs including user buttons movwf TRISB BANKSEL TRISC movlw b'11110000' ; LED lines as outputs movwf TRISC BANKSEL TRISD movlw b'00000000' ; LCD lines all are outputs movwf TRISD BANKSEL OPTION_REG movlw b'00000111' ; 0=PortB weak<7>,(Intedg<6>),(T0CS<5>),(T0SE<4>),(PSA<3>)25 6<210> movwf OPTION_REG ;;;; Initialize UART BANKSEL SPBRG ; Set up baud rate (9600) movlw .129 movwf SPBRG ; Set up serial port movlw 0x24 movwf TXSTA BANKSEL RCSTA ; Enable port movlw 0x90 movwf RCSTA BANKSEL PORTA ; Normal bank again

12th April 2004, 03:25 PM	#4
Exo	Can't see anything wrong with the setup code at first glance But you'll need to check TXIF before transmitting Code: Transmits W over the serial port SerialTransmit BANKSEL TXREG BTFSS PIR1, TXIF ;Buffer empty? GOTO $-1 ;no? then wait until it is MOVWF TXREG ;Transmit W RETURN