I am using UART in PIC16F877A with test board HJ-5G. My oscillator is 4MHz (KDS4.000). I tried to receive data from my computer.(Serial Debug Assistant) But I do not receive anything. And I tried to transmit data, but my Serial Debug Assistant can not receive anything. I use MPLAB X IDE v6.20 to run my code.
I have checked SPBRG. But I think I am right. I still don't know where is the problem. My RCREG is alaways 0x00.
INT_VECT:
movwf W_TEMP
movf STATUS, W
movwf STATUS_TEMP
BTFSC PIR1, 5
call uart_rx_isr
movf STATUS_TEMP, W
movwf STATUS
movf W_TEMP, W
RETFIE
uart_rx_isr:
movf RCREG, W
movwf RX_TEMP
bsf TEST_FLAGS, 0
bcf PIR1, 5
return
setup:
call uart_init
bsf STATUS, 5 ; select bank 1
CLRF TRISB
BSF TRISD, 2
bcf STATUS, 5 ; select bank 0
CLRF PORTB
movlw (1<<7)
IORWF INTCON
bcf STATUS, 0 ; clear carry
bcf INTCON, 0 ; clear int flag
; Debugging: Send initial status
movlw 'I'
movwf TXREG
call uart_tx_done
call send_debug_info
main:
; Reset receiver periodically
bcf RCSTA, 4 ; Disable receiver
bsf RCSTA, 4 ; Enable receiver
; Check for received data
BTFSS PIR1, 5
goto main_continue
; Read received data
movf RCREG, W
movwf RX_TEMP
bsf TEST_FLAGS, 0
; Echo received data
movf RX_TEMP, W
movwf TXREG
call uart_tx_done
uart_init:
bsf STATUS, 5 ; select bank 1
movlw 25 ; Set baud rate to 9600
movwf SPBRG
movlw 0b10000000 ; Set RC6 as output (TX) and RC7 as input (RX)
movwf TRISC
bcf STATUS, 5 ; select bank 0
movlw 0x90 ; Enable serial port and continuous receive
movwf RCSTA
bsf RCSTA, 4 ; CREN - Enable continuous receive
movf RCREG, W ; Clear receiver register
bsf STATUS, 5 ; select bank 1
movlw 0x24 ; Enable transmission
movwf TXSTA
bsf PIE1, 5 ; Enable receive interrupt
bsf INTCON, 7 ; Enable global interrupts
bsf INTCON, 6 ; Enable peripheral interrupts
bcf STATUS, 5 ; select bank 0
return
register value while I'm debugging
07/26 Now I simplified my whole code, I still don't know where is the problem. PORTD is connected to the LED.
#include <xc.inc>
; CONFIG
CONFIG FOSC = HS ; Oscillator Selection bits (HS oscillator)
CONFIG WDTE = OFF ; Watchdog Timer Enable bit (WDT disabled)
CONFIG PWRTE = OFF ; Power-up Timer Enable bit (PWRT disabled)
CONFIG BOREN = OFF ; Brown-out Reset Enable bit (BOR disabled)
CONFIG LVP = OFF ; Low-Voltage (Single-Supply) In-Circuit Serial Programming Enable bit (RB3 is digital I/O, HV on MCLR must be used for programming)
CONFIG CPD = OFF ; Data EEPROM Memory Code Protection bit (Data EEPROM code protection off)
CONFIG WRT = OFF ; Flash Program Memory Write Enable bits (Write protection off; all program memory may be written to by EECON control)
CONFIG CP = OFF ; Flash Program Memory Code Protection bit (Code protection off)
DELAY_A equ 0x70
DELAY_B equ 0x71
DELAY_C equ 0x72
W_TEMP equ 0x75
STATUS_TEMP equ 0x76
psect RESET_VECT,class=CODE,delta=2 ; PIC10/12/16
RESET_VECT:
goto setup
psect INT_VECT,class=CODE,delta=2 ; PIC10/12/16
INT_VECT:
movwf W_TEMP
swapf STATUS,W
movwf STATUS_TEMP
btfsc PIR1, 5
call uart_rx_isr
swapf STATUS_TEMP,W
movwf STATUS
movf W_TEMP,W
retfie
uart_rx_isr:
movf RCREG,0
movwf TXREG
bcf PIR1,5
return
setup:
bsf STATUS,5 ; select bank 1
movlw 25 ; Set baud rate to 9600 (assuming 4 MHz crystal)
movwf SPBRG
movlw 0b10000000 ; Set RC6 as output (TX) and RC7 as input (RX)
movwf TRISC
bcf STATUS,5 ; select bank 0
movlw 0x90 ; Enable serial port and continuous receive
movwf RCSTA
bsf STATUS,5 ; select bank 1
movlw 0x24 ; Enable transmission
movwf TXSTA
bsf PIE1,5 ; Enable receive interrupt
bsf INTCON,7 ; Enable global interrupts
bsf INTCON,6 ; Enable peripheral interrupts
bsf STATUS, 5
bcf TRISD, 0
bcf STATUS, 5
main:
bsf PORTD, 0
goto main
END
This is my all code and values. I can not receive RCREG value and this is related to Stop Bit. So my Serail Debug Assistant is not transmiting data ?
psect RESET_VECT,class=CODE,delta=2 ; PIC10/12/16 RESET_VECT: goto setup.