Hi,

some points besides for GIE (Olin said it the best way):

"The RCREG is a double buffered register ... [so it] can be read twice to
retrieve the two bytes in the FIFO. "

" ... transfers from the RSR register ... are inhibited, so it is
essential to clear error bit OERR if it is set."

(Cited from DS30390E, p. 108).

I hope this helps.

Regards,
Imre


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On Sat, 11 Aug 2001, Andy Meng wrote:

> Hello,
>
> I have been monitoring the PIClist for a few weeks, and decided to post
> about some trouble I am having with the USART on the 16F873. I have written
> some code to write to an LCD as the start of a larger project, and I am now
> working on the serial communications link. I first print the initialization
> message on the LCD, and send the same data out the USART to the PC at the
> same time. This works fine, but I can't transmit data back to the PIC from
> the PC.
>
> I am using a 16F873 running at 3.4MHz with a TC232 IC as the level
> converter. I checked the signals going into the PIC (on RC7) with a 'scope,
> and the levels appear to be fine. I am not sure about the actual bit
> pattern, but by going up and down the alphabet on the keyboard I can see
> binary counting going on, so I think it is sending the right data. I am
> using the old "Terminal" program, but I tried Hyperterminal also. It is
> running at 1200 baud. I have a troubleshooting LED that should turn on when
> it enters the ISR, but it never goes on when I send it characters. Below is
> the relevant part of the code:
>
> ------------------------------------------
>  org 0
>  goto Init
>
>  org 4
>  goto Interrupt
>
>  __CONFIG _BODEN_OFF & _CP_OFF & _XT_OSC & _PWRTE_OFF & _WDT_OFF & _LVP_OFF
>  include "P16F873.inc"
>
> Interrupt:
>     bcf           INTCON,GIE
>     btfss        INTCON,GIE
>     goto        $ - 2
>     bsf          PORTB,LED    ; turn on LED
>     call         Delay15ms
>     call         Delay15ms
>     call         Delay15ms
>     call         Delay15ms
>     bcf         PORTB,LED
>     btfsc      PIR1,RCIF       ; see if RX flag is set
>     call        RS232_Receive  ; if it is, call RS232_Receive
>     retfie
>
>     org 20
> Init:
>     clrf           INTCON            ; make sure INTCON is cleared
>     bsf           INTCON,PEIE   ; turn on interrupts for peripherals
>     movlw     0x90
>     movwf     RCSTA               ; turn on USART, continuous receive
>     bsf           STATUS,    RP0     ; page 1
>     clrf          PIE1                     ; clear individual peripheral
> interrupt enables
>     bsf          PIE1,RCIE          ; turn on USART RX interrupt
>     movlw     0x2B
>     movwf     SPBRG         ; load 1200 baud into baud rate gen
>     movlw     0x20
>     movwf     TXSTA         ; turn on serial transmit enable
>     bcf          STATUS,RP0     ; page 0
>     ; the rest of the LCD init code goes below this
>
> RS232_Receive:          ; called in ISR
>     movf       RCREG,w     ; put received data in w
>     movwf    RXdata          ; put it in RXdata reg
>     call         LCDwrite       ; write char to LCD
>     ;movf      RXdata,w      ; put data in w again
>     ;xorlw     0x0D             ; see if enter was pressed
>     ;btfsc      STATUS,0    ; if it was, go to next instruction
>     ;call        ClearLCD      ; clear the display
>     return
>
> ------------------------------------
>
> If I am doing something wrong, please let me know what it is and how I
> should change it.
>
> TIA,
>
> Andy Meng N8MX
>
> www.qsl.net/n8mx
>
>
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