Post by thread:Using RX interrupts with USART on PIC16C63

Hello, I am once again in the experimenting stage and have run into a wall........ I'm trying to communicate from one PIC16C63 to another PIC16C63 using the on-board USART with the rx used in interrupt mode. I'm running a loop where the contents of RAM is displayed on an LCD and the RX interrupt updates the ram. I am sending 12 characters every two seconds and from what I can see, it looks like only the 1st, 3rd, 5th, 7th, 9th, 11th, and 12th characters are received. I am using a 20MHz oscillator and running at 9600 baud (well actually 9469 baud with BRGH=0). My ISR is something like: ;---------------------------------------- ;RAM defines cblock rxbuffer:12 ;12 spaces reserved for rx buffer counter:1 ;counter for RX_ISR endc ;--------------------------------------- org 0x0000 goto start org 0x0004 goto ISR ;-------------------------------------- ;main program start ... ;initialization loop .... ;display contents of rxbuffer on LCD goto loop ;end of main program ;-------------------------------------- ISR .... ;disable further interrupts and save registers (w, status, fsr, pclath) call RX_ISR ... ;restore registers (pclath, fsr, status, w) retfie ;enable interrupts ;------------------------------------- RX_ISR movlw rxbuffer ;set up pointer movf fsr movlw 0x0c ;12 characters subwf counter,w btfss status,z ;check for zero goto $+2 ;if not zero, skip next line clrf counter ;reset counter movf counter,w ;get count addwf fsr ;point to location movf rcreg,w ;get character from rx fifo movwf indf ;store in rx buffer incf counter ;advance to next RAM location return Any comments are welcome. Am I missing something? Should I be handling the interrupt different. Oh, I did by the way do the initialization for interrupts on receive (async) and clear ram contents in the beginning. Thanks in advance! Randie spam_OUTrandie.ohtsjiTakeThisOuTglenayre.com

"Ohtsji, Randie" wrote: > > Is my interrupt routine too long? > > 9469 baud = 105uSec > > 20MHz = 50nSec x 4 clock/cycle = 200nSec per cycle > > Don't I have 500+ cycles to do stuff before receiving the next bit? > > Randie > .....randie.ohtsjiKILLspam.....glenayre.com > This is probably way off the mark, but are you sure your sending the Chars correctly ? The rx routine looks fine to me. I'm using similar routine on a 16c66 at 8Mhz 9600 baud with no problems at all. Have you sniffed the serial line with a PC to ensure all the data is being transmitted correctly ? -- ----------------------------------- Brad Campbell Technical Manager Seme Electrical Engineering Co 59 Collingwood St Osborne Park 6017 Western Australia Ph :-+61 8 9445 2577 Fax :-+61 8 9244 1327 Email :- EraseMEbradspam_OUTTakeThisOuTseme.com.au /"\ \ / X ASCII RIBBON CAMPAIGN / \ AGAINST HTML MAIL

Out of 12 characters, I do properly receive the 1st, 3rd, 5th, 7th, 9th, 11th, and 12th character. On the scope, transmit looks okay. On the transmitter side I am doing a routine similar to (just off the top of my head): tx_send movlw 0x0c ;12 characters to send movwf txcounter movlw txbuffer ;set up pointer movwf fsr tx_out: movf indf,w ;get character to send movwf txreg btfss pir1,txif ;check transmit buffer goto $-1 ;wait, transmit buffer not empty yet incf fsr ;advance pointer to next RAM decfsz txcounter goto tx_out return Randie randie.ohtsjispam_OUTglenayre.com > {Original Message removed}

Ohtsji, Randie wrote: {Quote hidden}> > Out of 12 characters, I do properly receive the 1st, 3rd, 5th, 7th, 9th, > 11th, and 12th character. > On the scope, transmit looks okay. > > On the transmitter side I am doing a routine similar to (just off the top of > my head): > > tx_send > movlw 0x0c ;12 characters to send > movwf txcounter > movlw txbuffer ;set up pointer > movwf fsr > tx_out: > movf indf,w ;get character to send > movwf txreg > btfss pir1,txif ;check transmit buffer > goto $-1 ;wait, transmit buffer not empty yet > incf fsr ;advance pointer to next RAM > decfsz txcounter > goto tx_out > return I had the same problem until I checked TXSTA,TRMT instead of PIR1,TXIF. Transmit movwf TXREG bsf STATUS,RP0 txddn btfss TXSTA,TRMT goto txddn bcf STATUS,RP0 return

Hi, maybe you do not have the problem I will describe, but I had it: (excerpt from data sheet): "Overrun bit OERR has to be cleared in software. This is done by resetting the receive logic (CREN is cleared and the set). If bit OERR is set, transfers ... are inhibited, so it is essential to clear error bit OERR if it is set." It means also "it is essential for the user to read the RCSTA register before rading RCREG register". After I did everything went o. k. I hope this helps. Imre On Mon, 23 Nov 1998, Ohtsji, Randie wrote: {Quote hidden}> Hello, > > I am once again in the experimenting stage and have run into a wall........ > > I'm trying to communicate from one PIC16C63 to another PIC16C63 using the > on-board USART with the rx used in interrupt mode. > I'm running a loop where the contents of RAM is displayed on an LCD and the > RX interrupt updates the ram. I am sending 12 characters every two seconds > and from what I can see, it looks like only the 1st, 3rd, 5th, 7th, 9th, > 11th, and 12th characters are received. > > I am using a 20MHz oscillator and running at 9600 baud (well actually 9469 > baud with BRGH=0). > > My ISR is something like: > > > ;---------------------------------------- > ;RAM defines > > cblock > rxbuffer:12 ;12 spaces reserved for rx buffer > counter:1 ;counter for RX_ISR > endc > > > ;--------------------------------------- > org 0x0000 > goto start > > org 0x0004 > goto ISR > > ;-------------------------------------- > ;main program > > start > ... ;initialization > loop .... ;display contents of rxbuffer on LCD > goto loop > > ;end of main program > > > ;-------------------------------------- > ISR > .... ;disable further interrupts and save > registers (w, status, fsr, pclath) > call RX_ISR > ... ;restore registers (pclath, fsr, status, w) > retfie ;enable interrupts > > > ;------------------------------------- > RX_ISR > movlw rxbuffer ;set up pointer > movf fsr > movlw 0x0c ;12 characters > subwf counter,w > btfss status,z ;check for zero > goto $+2 ;if not zero, skip next line > clrf counter ;reset counter > movf counter,w ;get count > addwf fsr ;point to location > movf rcreg,w ;get character from rx fifo > movwf indf ;store in rx buffer > incf counter ;advance to next RAM location > return > > Any comments are welcome. Am I missing something? Should I be handling the > interrupt different. > Oh, I did by the way do the initialization for interrupts on receive (async) > and clear ram contents in the beginning. > > Thanks in advance! > > Randie > @spam@randie.ohtsjiKILLspamglenayre.com > >