Debug @ 9600 on 4Mhz 16F676

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- 11th March 2007, 12:25
sougata

Debug @ 9600 on 4Mhz 16F676

Hi,

I am working with a project on a 16f676. It is running on its internal 4MHz RC oscillator. It is using extensive interrutps. (Tmr0, Tmr1, INTF, Comparator). All of the interrupt routines are in ASM. Almost all pins are used. For debugging prupose I need to view a few registers. Only option is to use debug on one of the LED indicator.

Now my question is what is the Maximum Baud Rate usable ? PBP manual says that for SEROUT2 oscillators greater than 4MHz :confused: may be required for more than 4800bps.
- 11th March 2007, 15:26
Darrel Taylor

From Bruce,

Serial Baudrate 115200
http://www.picbasic.co.uk/forum/show...64&postcount=2
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- 11th March 2007, 16:47
sougata

Thanks Darrel for the info.

Hi,

Thank you very much Darrel. I have already successfully used it at 9600. This gives me enough courage and confidence to use it at 115200.
- 11th March 2007, 16:56
Bruce

That post was in error, but there was no way to change it. You can get up
to 19200 bps with a 4MHz osc with PBP's DEBUG.

Someone mentioned the error, but it wouldn't allow me to change it.

However, you definitely can get up to 115200 bps with a 4MHz osc, but you'll
need to use assembler. Try this;

Code:

processor 16F876a #include <P16F876a.inc> errorlevel -302 ; suppress "not in bank 0" message ; Defines #define TxPin PORTC,6 ;define serial TX pin #define bank1 banksel 0x80 ;select bank 1 #define bank0 banksel 0x00 ;select bank 0 ; variable allocations cblock 0x20 ;start at RAM location 20h Counter ;bit counter TxByte ;holds byte to transmit MsgPtr ;message character pointer offset CharCnt ;number of characters in text message dlyLSD ;for delay loop endc org 0x00 ;reset vector goto Main org 0x05 ;required for MCS loader Main call Init ;init port MsgLoop movlw .17 ;17 characters in the message movwf CharCnt ;load character count movlw .0 ;pointer offset to 1st char in table movwf MsgPtr ;load character pointer NextChar movf MsgPtr,w ;load char pointer into W reg call Message ;fetch character from table call TxRoutine ;send it incf MsgPtr,f ;increment char pointer decfsz CharCnt,f ;decrement char count, skip if done goto NextChar ;not finished, then fetch next char call Delay_50uS ;short delay between messages goto MsgLoop ;continuous loop Message ;prints Hello World....!<CR> addwf PCL,f ;load character offset retlw 'H' ;return with ASCII character in W reg retlw 'e' retlw 'l' retlw 'l' retlw 'o' retlw ' ' retlw 'W' retlw 'o' retlw 'r' retlw 'l' retlw 'd' retlw '.' retlw '.' retlw '.' retlw '.' retlw '!' retlw '\r' ;carriage return tagged onto end of message TxRoutine movwf TxByte ;load byte to send into TxByte movlw .8 ;preload bit counter with 8 movwf Counter StartBit bcf TxPin ;true mode / low for START bit goto $+.1 ; 2uS goto $+.1 ; 2uS nop TxLoop rrf TxByte,f ;rotate into carry / send LSB first btfsc STATUS,C ;if bit = 1 then goto SetBit ;send a 1 bcf TxPin ;else send a 0 goto $+.1 ;2uS decfsz Counter,f ;decrement bit count goto TxLoop ;if not 0, then continue goto StopBit+.2 ;else send stop bit SetBit bsf TxPin ;send 1 nop decfsz Counter,f goto TxLoop StopBit nop goto $+.1 ;2uS goto $+.1 ;2uS bsf TxPin ;begin stop bit period goto $+.1 ;2uS goto $+.1 ;2uS return ;2uS rest of program handles the rest Init bank0 movlw b'01000000' ;TX pin idles high (true mode) movwf PORTC ;set port latches bank1 ;bank 1 movlw b'10000000' ;RX in, rest outs movwf TRISC ;set port directions bank0 ;back to bank 0 return Delay_50uS ;call + delay + return = 50uS movlw .15 ;at 4MHz movwf dlyLSD decfsz dlyLSD, f goto $ - .1 return end
- 12th March 2007, 01:26
sougata

Thanks Bruce

Hi,

Thank you Bruce for your ASM routine. This would make my life a lot more easier. Since I have interrupts running around I was worried that if my serial transmission gets interrupted too often then I would have large timing error. Now with your ASM routine I can stuff it in inside my INT Handler since I am already having a timebase running.

One more question :o ?

Since I am using hyperterm I am restricted to :confused: ASCII transmission. For example say I need to watch a variable. Using DEBUG with the # modifier sends an "ASCII" representation. This increases the tx overhead. Is there anyway I can view the Binary value of the Tx Data. All I need is an automatically linefeed display of the incoming byte on my PC.
- 12th March 2007, 13:06
Bruce

Hi Sougata,

I'm not sure how to do that with HyperTerm. Displaying a single byte value in
binary sends an ASCII 1 or 0 byte-per-bit. You would probably need to write
your own serial terminal program for something like that.
- 12th March 2007, 14:51
sougata

Thanks Again

Hi,

I am not that experienced on the PC side programming but then again your site provides excellent startup pointers. http://www.rentron.com/VisualBasic.htm

So thanks again for the insight.