I've been happily using a PIC 16F628A UART for some time now. I've switched up to a PIC 18F4431 chip recently but having some problems with the USART. Initially I couldn't get the transmit function to work, it was transmitting but at only 0.8V for high condition. Strangely I then put in these lines:
movlw 0FFh
movwf PORTB
and suddenly it started transmitting correctly and I can receive data OK via the UART on Pickit2. Unfortunately I now cannot receive anything via the UART. I've tried multiple chips and they all exhibit the same behaviour.
I've attached my code below, any ideas??
include <P18f4431.INC>
CONFIG OSC = IRC
CONFIG FCMEN = OFF
CONFIG IESO = OFF
CONFIG PWRTEN = OFF
CONFIG BOREN = OFF
CONFIG BORV = 20
CONFIG WDTEN = OFF
CONFIG WDPS = 1
CONFIG WINEN = OFF
CONFIG PWMPIN = OFF
CONFIG LPOL = LOW
CONFIG T1OSCMX = OFF
CONFIG FLTAMX = RC1
CONFIG SSPMX = RD1
CONFIG PWM4MX = RB5
CONFIG EXCLKMX = RC3
CONFIG MCLRE = ON
CONFIG CP0 = OFF
CONFIG CP1 = OFF
CONFIG CP2 = OFF
CONFIG CP3 = OFF
CONFIG CPD = OFF
CONFIG WRT1 = OFF
CONFIG WRT2 = OFF
CONFIG WRT3 = OFF
CONFIG WRTC = OFF
CONFIG WRTB = OFF
CONFIG WRTD = OFF
CONFIG EBTR0 = OFF
CONFIG EBTR1 = OFF
CONFIG EBTR2 = OFF
CONFIG EBTR3 = OFF
CONFIG EBTRB = OFF
CONFIG HPOL = LOW
CONFIG STVREN = OFF
CONFIG DEBUG = OFF
CONFIG CPB = OFF
CONFIG WRT0 = OFF
CONFIG LVP = OFF
;***********VARIABLE DEFINITIONS******************
Timer res 1
Timer2 res 1
DataTemp1 res 1
DataTemp2 res 1
dataL res 1
;*******************************************************************************
; Reset Vector
;*******************************************************************************
STARTUP CODE 0x00 ; processor reset vector
GOTO START ; go to beginning of program
org 0x0008
GOTO HIGH_ISR
;*******************************************************************************
; MAIN PROGRAM
;******************************************************************************
PROG1 code
START
clrf PORTD
clrf TRISD
clrf LATB ; clear portB output latches
clrf TRISB ; set all portB as outputs
clrf TRISC ;set all port C as outputs
;***********SET UP USART ***********************
bsf TRISC, 7 ; Make RC7 an input
bsf TRISC, 6
bsf TRISC, 1
movlw d'12' ;9600 baud at 8MHz
movwf SPBRG
bsf TXSTA, TXEN ; enable transmit
bcf TXSTA, BRGH ;de Select high baud rate
bsf RCSTA, SPEN ; enable serial port
bsf RCSTA, CREN ; Enable continuous reception
bcf PIR1, RCIF ; clear RCIF Interrupt Flag
bsf PIE1, RCIE ; Set RCIE Interrupt Enable
bsf INTCON, PEIE ; Enable peripheral interrupts
bsf INTCON, GIE ; Enable global interrupts
movlw 0FFh
movwf PORTB ; I don't know why I need to do this but this seems to be
; needed to kick start the USART !!!!!
;***********SET UP OSCILLATOR**************
bsf OSCCON, IRCF0
bsf OSCCON, IRCF1
bsf OSCCON, IRCF2
;***********MAIN ROUTINE **********************************
;********SETTLING TIME *************
clrf dataL
settle: decfsz dataL, F
goto settle
;*******flush the receive buffer**************
movf RCREG, w
movf RCREG, w
movf RCREG, w
;turn on lamp to show power
bsf PORTD, 1
Loop:
call Delay
GOTO Loop ; loop forever
Delay:
movlw d'255'
movwf Timer
movwf Timer2
Loop2:
nop
Loop1:
nop
decfsz Timer, f
goto Loop1
decfsz Timer2, f
goto Loop2
return
HIGH_ISR
btfss PIR1, RCIF ;check if USART caused interrupt
goto OtherInt
btg PORTD, 0
movlw 06h ; mask unwanted bits
andwf RCSTA,w ;check for errors
btfss STATUS,Z ;was error status bit set?
goto RCVError ; Found error goto handler
movf RCREG, w ; get input data and stick it on w
movwf LATB ; Display on LEDs
movwf TXREG ; Echo character back
goto ISREnd ; go to end of ISR, restore context, return
RCVError
bcf RCSTA, CREN ; clear receiver status
bsf RCSTA, CREN
movlw 0FFh ; light all the LEDs
movwf PORTB
goto ISREnd ; goto end of ISR
OtherInt
ISREnd
RETFIE
END
