I'm trying to use the USART from a 16C65 to talk to a PC's RS2. I've put
inputs in the RC7 pin in the MPLAB with an stimulus file and with
Asynchornous stimulus, but no char gets in. The code I use to initialize the
USART is:

RS2inic bsf     STATUS,RP0 ;                 *** Banco 1 ***
        movlw   D'25'      ; 9600 Baud
        movwf   SPBRG
        movlw   B'00100100'
                ;  ||| +--> BRGH=1 High speed
                ;  ||+----> SYNC=0 Async. transmission
                ;  |+-----> TXEN=1 Enable transmission
                ;  +------> TX8/9=0 8 bits/byte transmission
        movwf   TXSTA
        bcf     STATUS,RP0 ;                 *** Banco 0 ***
        movlw   B'10010000'
                ; || +----> CREN=1 Enable reception
                ; |+------> RC8/9=0 8 bits/byte reception
                ; +-------> SPEN=1 Enable serial port
        movwf   RCSTA

And then I wait Interruptions from the USART each incoming char.

The Interruptions initialization is as follows:

; Inicializa las interrupciones
INTinic clrf    PIR1       ; TMR2IF=0 Erase int flags
        movlw   B'00110010'
                ;   ||  +--> TMR2IE=1 -> Enable tmr2 int.
                ;   |+-----> TXIE=1 -> Enable transm. int.
                ;   +------> RCIE=1 -> Enable receip. int.
        bsf     STATUS,RP0 ;                 *** Banco 1 ***
        movwf   PIE1
        bcf     STATUS,RP0 ;                 *** Banco 0 ***
        bsf     INTCON,6   ; PEIE=1 -> Enable perif. int.
        bsf     INTCON,7   ; GIE=1  -> Enable general int.
        return

(I use a constant timer int and both In and Out USART ints)

ÀWhat's wrong?

Thanks in advance.

-----Mensaje original-----
De: Tom Handley <thandley@TELEPORT.COM>
Para: PICLIST@MITVMA.MIT.EDU <PICLIST@MITVMA.MIT.EDU>
Fecha: miŽrcoles, 05 de mayo de 1999 14:19
Asunto: Re: PIC16c74


>   Aidi, SREN is not relevant in the Asynchronous mode so there is no need
>to clear it. What probably fixed your problem is the clearing and setting
of
>the CREN bit which clears the Overrun Error bit, OERR. A better way to
>handle this is to monitor OERR and FERR (Framing Error). If OERR is set,
>clear the error by clearing and setting the CREN bit. If FERR is set, clear
>the error by reading another Byte from the RCREG. While I normally use
>Parallax/CVASM syntax I can provide a MPASM example if someone else does'nt
>jump in.
>
>   This leads to a more serious problem. The 16C74 and 16C74A have a known,
>documented, bug when using the high-speed mode (BRGH=1). You simply can not
>get reliable operation with these devices (and the 16C73/73A) when BRGH=1.
>The simple and low cost solution is to use another crystal. With an 8MHz
>crystal you can get 9600 +/- 0.16% with BRGH=0 and SPBRG=12. You can also
>switch to a 16C74B or a 16C77 which work fine with BRGH=1. They are both
>pin-compatible with the 16C77 having 8K of program memory and 368 Bytes of
>data memory compared with 4K/192 Bytes for the 16C74x. Another nice thing
>about the 16C77 is that the upper 16 Bytes of data memory are mapped into
>all four banks.
>
>   - Tom
>
>At 02:24 PM 5/4/99 -0400, Aidi Moubhij wrote:
>>Hi Ray,
>>Thank you very much for your help.  What you suggested fixed the problem.
>>Now I can move on to the next step.  Thank you again.
>>
>>At 01:08 PM 5/4/99 -0400, Ray Gardiner wrote:
>>>Hi Aidi,
>>>Just a couple of things, you should set CREN before clearing SREN,
>>>I also found that toggling CREN after receive to clear any rx errors.
>>>See code below. You also must wait for the byte to actually be received.
>>>
>>>> Hi,
>>>>
>>>>I'm using the code below to receive a byte from the US ART. When I get
the
>>>>byte I display it on the LED's and echo it back.
>>>>This code is not working for me.  Can anybody tell me what I'm doing
wrong.
>>>> Thanks
>>>>
>>>> list p=16c74
>>>>        Title "first aidi Program"
>>>>
>>>>        include <P16C74.INC>
>>>>
>>>>        org     00h
>>>>
>>>>Start
>>>>    clrf    PORTB           ;Clear PORT_B output latches
>>>>
>>>>        bsf     STATUS,RP0      ;Go to Bank1
>>>>
>>>>        clrf    TRISB           ;Config PORT_B as all outputs
>>>>
>>>>
>>>>        movlw   19h             ;Set Band rate (9600 baud @4MHz)
>>>>        movwf   SPBRG
>>>>        movlw   b'00100100'     ;8-bit transmit, transmitter enable
>>>>        movwf   TXSTA           ;Asynchronous mode, High baud rate
>>>>
>>>>        bcf     STATUS,RP0      ;Go to Bank0
>>>>
>>>>        movlw   b'10010000'     ;8-bit receive, receiver enabled
>>>>        movwf   RCSTA           ;serial port enabled
>>>>
>>>
>>>; ADDED THE FOLLOWING LINES *****;
>>>                                 ;
>>>RxTest                           ;
>>>                                 ;
>>>         BSF     RCSTA,4         ;set CREN
>>>         BCF     RCSTA,5         ;clear SREN
>>>                                 ;
>>>RxWait                           ;
>>>         BTFSS   PIR1,5          ;RxBuffer Full when PIR,5=1
>>>         GOTO    RxWait          ;
>>>                                 ;
>>>         BCF     RCSTA,4         ;toggle CREN to clear any Rx
>>>         BSF     RCSTA,4         ;errors. You could choose to
>>>                                 ;handle Rx errors differently
>>>                                 ;for a "real" application.
>>>; *******************************;
>>>
>>>>        movf    RCREG,W         ;Get input data
>>>>        movwf   PORTB           ;Display on LEDs
>>>>        movwf   TXREG           ;Echo character back
>>>
>>>>        goto    RxTest          ; ***Changed here also.
>>>>
>>>>        end
>>>
>>>>Aidi Moubhij
>>>Ray Gardiner ray@hdc.com.au
>>Aidi Moubhij
>