I am using port b to trouble shoot.

Everything works fine until I add the rx_loop2

rx_loop is used to filter out all characters entered via RS232 except the
letter 'a'

If the letter 'a' is choosen I want to then proceed to rx_loop2 and wait for
the next
character to be entered via RS232, then proceed to tx_loop and send the
contents of the w register.

My problem is that when I enter the letter 'a' the program proceeds thru
rx_loop2 and tx_loop.

I have tried to clear the interupt Flag PIR1 , RCIF but that doesn't seem to
work

I am new at this PIC stuff and after 2 days, I am at a loss!

Does anybody have any ideas?



    Title  "RS232 Port"
     ;
     list p=16f877,c=140    ; processor type
     errorlevel          1, -(305)
     #include "p16f877.inc"
;
; CONFIGURATION BITS:
;
;    Oscillator           = HS
;    Watchdog Timer       = Off
;    Power Up Timer       = On
;    Code Protect         = Off
;    Brown Out Detect     = On
;    Low Voltage Program  = Disabled
;    Data EE Protect      = Off
;    Flash Program Write  = Enabled
;    Background Debug     = Disabled
;
;
; DESCRIPTION:
;
; Baud Rate = 9600, No Parity, 8 bits & 1 Stop Bit, Hardware = None
;
;    RS232 | MAX233          MAX233 | 16F877
;    --------------          ---------------
;     2-RX | 5-TX              2-TX | 25-TX
;     3-TX | 4-RX              3-RX | 26-RX
;
; PROGRAM START:
;
     org  0                             ; startup = 0000H
     clrf STATUS                        ; bank 0
     call main
     goto start_com
     org  4
ISR  goto 5
     org  5
;
main
;
     call setup_ports
     call setup_usart
     call blink
;
     return
;
setup_ports
;
     banksel PORTA                      ; bank0
     movlw     b'00000000'
     movwf     PORTA
     movlw     b'00000000'
     movwf     PORTB
     movlw     b'01000000'
     movwf     PORTC
     movlw     b'00000000'
     movwf     PORTD
     movlw     b'00000000'
     movwf     PORTE

     banksel TRISA                      ; bank1
     movlw     b'00000000'
     movwf     TRISA
     movlw     b'00000000'
     movwf     TRISB
     movlw     b'11000000'      ; set RC6 & RC7 as input
     movwf     TRISC
     movlw     b'00000000'
     movwf     TRISD
     movlw     b'11111000'
     movwf     TRISE
     movlw     b'00000111'
     movwf     ADCON1           ; PORTA inputs = digital not analog
;
     return
;
setup_usart
                                        ; Baud Values with BRGH = 1
                                        ; ((20000000/9600)/16)-1 = 32
     movlw     d'129'           ; 9600 baud @ 20 Mhz Fosc +0.16 err
     movwf     SPBRG
     movlw     b'00100100'      ; brgh = 1
     movwf     TXSTA            ; enable Async Transmission, set brgh
     banksel   RCSTA                    ; bank0
     movlw     b'10010000'
     movwf     RCSTA            ; enable Async Reception
     movf      RCREG,w
     movf      RCREG,w
     movf      RCREG,w          ; flush receive buffer
;
     return
;
start_com
     call      rx_loop          ; wait and read from RS232
     call      clear_rcif
     call      rx_loop2
;
tx_loop
     nop
     btfss     PIR1,TXIF                ; xmit buffer empty?
     goto tx_loop                       ; no, wait
;
     movwf     TXREG
;
     goto start_com                     ; no
;
; RECEIVE CHARACTER FROM RS232
;
rx_loop
     nop
     btfss     PIR1, RCIF               ; check for received data
     goto rx_loop
;
     bcf PIR1, RCIF
;
     movf RCREG,w
     sublw 'a'
     btfss STATUS, Z
     goto rx_loop
;
     bcf STATUS,Z
;
     movlw 01h                  ;If led on RB0 is on, an 'a' has been
entered
     movwf PORTB
;
     return
;
clear_rcif
     bcf PIR1, RCIF
     btfsc PIR1, RCIF
     goto clear_rcif
;
     movlw 02h                  ;If led on RB1 is on, a second character has
been received
     movwf PORTB
;
     return
;
rx_loop2
     nop
     btfss     PIR1, RCIF               ; check for received data
     goto rx_loop2
;
     return
;
blink                                           ; Show sign of life by
blinking RB0 twice
;
     movlw 01h
     movwf PORTB
;
     call Delay500
;
     movlw 00h
     movwf PORTB
;
     call Delay500
;
     movlw 01h
     movwf PORTB
;
     call Delay500
;
     movlw 00h
     movwf PORTB
;
     return
;
Delay500
;
DelayL  equ     0x20                    ; delay register LOW byte
DelayM  equ     0x21                    ; delay register MID byte
DelayH  equ     0x22                    ; delay register HIGH byte
;
      clrf              DelayL          ; /R clear DelayL to 0
        clrf            DelayM          ; clear DelayM to 0
        movlw   6h                      ; set DelayH to 12
        movwf   DelayH
Wait1 decfsz    DelayL          ; subtract 1 from DelayL
        goto            Wait1           ; if not 0, goto Wait1
        decfsz  DelayM          ; subtract 1 from DelayM
        goto            Wait1           ; if not 0, goto Wait1
        decfsz  DelayH          ; subtract 1 from DelayH
        goto            Wait1           ; if not 0, goto Wait1
;
     return
;
     end

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