This document contains code for receiving and transmitting a byte using USART on a PIC microcontroller. The receiving code section initializes ports and registers for USART reception. It then enters a loop to continuously clear the watchdog timer. When a byte is received, it is moved from the receive register to a data variable and output on port B. The transmitting code initializes ports for output, reads the byte from port B, and calls a subroutine to transmit the data. The subroutine sets up transmission parameters and loads the data byte into the transmit register to be sent via USART. It then waits for transmission to complete before returning.

1. ;***********************************************
;***RECEPCIÓN DE UN BYTE MEDIANTE USART***
;***********************************************
LIST P=16F873
INCLUDE P16F873.INC
W_TEMP EQU 20H
STATUS_TEMP EQU 21H
DATOB EQU 22H
ORG 00H
GOTO INICIO
ORG 04H
GOTO INTER
INTERBCF INTCON,7
movwf W_TEMP
swapf W_TEMP,1
movf STATUS,0
movwf STATUS_TEMP
BTFSS PIR1,RCIF
GOTO VOLVER
MOVF RCREG,0
MOVWF DATOB
MOVF DATOB,0
MOVWF PORTB
BCF PIR1,RCIF
VOLVER movf STATUS_TEMP,0
movwf STATUS
swapf W_TEMP,0
BSF INTCON,7
RETFIE
INICIO CLRWDT
CLRF PORTB
CLRF PORTC
BSF STATUS,5
BCF STATUS,6
MOVLW B'00000000'
MOVWF TRISB
MOVLW B'10111111'
MOVWF TRISC

2. MOVLW B'00100100'
MOVWF TXSTA
MOVLW D'25'
MOVWF SPBRG
BSF PIE1,RCIE
BCF STATUS,5
BCF STATUS,6
MOVLW B'10010000'
MOVWF RCSTA
MOVLW B'11000000'
MOVWF INTCON
BUCLE CLRWDT
GOTO BUCLE
END
;*******************************************
;***TRANSMISIÓN DE UN BYTE MEDIANTE USART***
;*******************************************
LIST P=16F873
INCLUDE P16F873.INC
DATOB EQU 20H
ORG 00H
GOTO INICIO
ORG 04H
RETFIE
INICIO
BSF STATUS,6
BSF STATUS,5
MOVLW B'11111111'
MOVWF TRISB
BCF STATUS,6
MOVLW B'10000000'
MOVWF TRISC
PASO1
BCF STATUS,6
BCF STATUS,5

3. MOVF PORTB,0
MOVWF DATOB
CALL ENVIAR_DATO
GOTO PASO1
ENVIAR_DATO
BCF STATUS,6
BSF STATUS,5
MOVLW B'00100110'
MOVWF TXSTA
MOVLW D'25'
MOVWF SPBRG
BCF STATUS,5 ;Banco0
BSF RCSTA,7 ;SPEN=1 ON USART
MOVF DATOB,0
MOVWF TXREG
ESPERA BTFSS PIR1,4
GOTO ESPERA
RETURN
END