This document contains code for receiving and transmitting a byte using USART on a PIC microcontroller. It defines registers for the status, data byte, and other variables. The receive routine checks for received data and stores it. The transmit routine continuously reads the port and sends the value. It also includes delay routines to add timing.

1. ;**************************************************************
;***RECEPCIÓN DE UN BYTE MEDIANTE USART***
;**************************************************************
LIST P=16F873A
INCLUDE P16F873A.INC
W_TEMP EQU 20H
STATUS_TEMP EQU 21H
DATOB EQU 22H
ORG 00H
GOTO INICIO
ORG 04H
INTER BCF 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
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

2. BUCLE CLRWDT
GOTO BUCLE
END
;*******************************************
;***TRANSMISIÓN DE UN BYTE MEDIANTE USART***
;*******************************************
LIST P=16F873A
INCLUDE P16F873A.INC
DATOA EQU 20H
PDel0 EQU 27H
PDel1 EQU 28H
PDel2 EQU 29H
ORG 00H
GOTO INICIO
ORG 04H
RETFIE
INICIO BCF STATUS,6
BSF STATUS,5
MOVLW B'00000110'
MOVWF ADCON1
MOVLW B'11111111'
MOVWF TRISA
MOVLW B'10000000'
MOVWF TRISC
MOVLW B'00100110'
MOVWF TXSTA
MOVLW D'25'
MOVWF SPBRG
BCF STATUS,5 ;Banco0
BSF RCSTA,7 ;SPEN=1 ON USART
NUEVODATO
MOVF PORTA,0
MOVWF DATOA
CALL ENVIAR_DATO
GOTO NUEVODATO
ENVIAR_DATO
MOVF DATOA,0
MOVWF TXREG
ESPERA BTFSS PIR1,4
GOTO ESPERA
CALL DEMORA
RETURN
;RETARDO DE 5 SEGUNDOS, extraída del PICDEL
DEMORA movlw .165 ; 1 set numero de repeticion (C)
movwf PDel0 ; 1 |
PLoop0 movlw .41 ; 1 set numero de repeticion (B)
movwf PDel1 ; 1 |

3. PLoop1 movlw .147 ; 1 set numero de repeticion (A)
movwf PDel2 ; 1 |
PLoop2 clrwdt ; 1 clear watchdog
clrwdt ; 1 ciclo delay
decfsz PDel2, 1 ; 1 + (1) es el tiempo 0 ? (A)
goto PLoop2 ; 2 no, loop
decfsz PDel1, 1 ; 1 + (1) es el tiempo 0 ? (B)
goto PLoop1 ; 2 no, loop
decfsz PDel0, 1 ; 1 + (1) es el tiempo 0 ? (C)
goto PLoop0 ; 2 no, loop
return ; 2+2 Fin.
END
;Rutina BIN_BCD. ESTUDIAR SU APLICACIÓN
BIN_BCD NOP
BCDCEN movlw d'100'
subwf DATOB,1
btfsc STATUS,0
goto SUBE
goto SIGUE_DEC
SUBE incf CEN,1
goto BCDCEN
SIGUE_DEC movlw d'100'
addwf DATOB,1
BCDDEC movlw d'10'
subwf DATOB,1
btfsc STATUS,0
goto SUBE2
goto SIGUE_UNI
SUBE2 incf DEC,1
goto BCDDEC
SIGUE_UNI movlw d'10'
addwf DATOB,1
BCDUNI movlw d'1'
subwf DATOB,1
btfsc STATUS,0
goto SUBE_UNI
goto SIGUE
SUBE_UNI incf UNI,1
goto BCDUNI
SIGUE return
;RUTINA BCD_ASCII. ESTUDIAR SU APLICACIÓN
BCD_ASC MOVLW 30H
ADDWF CEN,0
MOVWF ASCIIB2
MOVLW 30H
ADDWF DEC,0
MOVWF ASCIIB1
MOVLW 30H
ADDWF UNI,0
MOVWF ASCIIB0
RETURN