Hi,

I'm, trying to do flow control, using PORTA,6 to signal that the pic is
ready to recieve data.

pseudocode is:

interrupt handler:
set PORTA,6 high
retfie

main loop:          //wait for interrupt handler
if PORTA,6 is low
goto main loop
else
set PORTA,6 low
get the byte out of RCREG
//do things with it... not written yet
goto main loop

The result of running this is that when I send a byte, PORTA,6 goes high,
but it never goes low again, ever.  I've used the same initialisation for
the usart registers in other working programs, so i know i've got that bit
right.

This is driving me mad, what have I missed??
Thanks
Nick

full code:

    list p=16f628a
    include "p16f628a.inc"

    __CONFIG 0x3f10

    org        0x0000
    goto    main

    org        0x0004
    goto    isr

    org     0x0005

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; begin here
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

main
    ; initialisation:
    ;i/o ports
    MOVLW    0x07
    MOVWF    CMCON
    CLRF    PORTA
    MOVLW    0x01
    MOVWF    PORTB
    bsf        STATUS,RP0
    CLRF    TRISA
    MOVLW    0x0a
    MOVWF    TRISB

    ;interrupts
    MOVLW    0x20
    MOVWF    PIE1
    MOVLW    0xc0
    MOVWF    INTCON

    ;usart
    MOVLW    0x19
    MOVWF    SPBRG
    MOVLW    0x24
    MOVWF    TXSTA
    bcf        STATUS,RP0
    MOVLW    0x90
    MOVWF    RCSTA

    call delay

    movf RCREG,W
    movf RCREG,W
    movf RCREG,W    ; flush receive buffer

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; main
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

start
    btfss    PORTA,6
    goto     start

    MOVF    RCREG,W
    bcf        PORTA,6
    ; do stuff

    goto    start

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; isr
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;

isr
    bsf        PORTA,6
    bcf        RCSTA,4    ;clear overrun
    bsf        RCSTA,4
    retfie
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