Microchip PIC Delay Code Generator

For long delays (> 10 cycles) the code is based on nested loops using 'decfsz' and 'goto' instructions. Small delays are built using 'goto $ + 1' (2 cycles delay) and 'nop' (one cycle delay).

To calculate nested loop counter values the code generator uses an optimum search algorithm. The algorithm finds such values for counters that achieve good approximation to the specified delay.

Even if there is an error in the first block of nested loops, the rest of the code fixes that. As a result, one cycle resolution is achieved.

Idea: James Newton
Implementation: Nikolai Golovchenko

This application is mirrored at:

• https://www.golovchenko.org/home/delay_loops

Also:

• Multiplication and division by a constant 
• Keyword matching in a serial text stream
• Convert Binary to Decimal for A2D Converter output
• The character set extractor

See:

• PIC Specific delays
• SX Specific delays
• /techref/microchip/12ceeprom.htm proper initialization delays for 12cxxx EEPROM access

See also:

• http://www.disall.narod.ru/prog.htm PIC Delay routine
• http://www.mnsi.net/~boucher/picloops.html
• http://www.golovchenko.org/cgi-bin/delay

Questions:

• finn.jensen at spamlive.de asks:

  I'd like to know how exactly I have to calculate the loop. I know my time I want to have and put it in the generator, but when I want to calculate with my variables I don't know how to put those together. I know that for a single loop like this one movlw D'3' movwf d1 decfsz d1,f goto $-1 I have to calculate 3*d1-1. But if I have a nested loop like this one: movlw D'3' movwf d1 movlw D'4' movwf d2 decfsz d1,f goto $-1 decfsz d2,f goto $-3 I don't know how to calculate it! is it (3*d1-1)*(3*d2-1) ? I'd like to get a formula for that!

  +

Interested:

Daniel Chia Jin Hao Says:

For PIC18, this delay routine will need a little modification to work properly.. the goto $+1 within the delay loops that sometimes appears needs to be changed to goto $+6, since each program word is 2 bytes, and goto is a 4 byte instruction. Also, at the end sometimes goto $+1 is used as a 2 cycle delay, need to use goto $+4 to skip over the whole goto.

I hope this is correct, AFAIK it is.

Comments:

• ardv at spamoutlook.com " i hope that you make a code without "goto $"" +
• ptdpublic at spammac.com " This is very cool. I've included link back to this generator in comments and provided credit in my code. thank you" +
• WOW Exellent Idea, Excellent Implementation!!