In SX Microcontrollers, SX/B Compiler and SX-Key Tool, PJMonty wrote:

Electro,

Here's the routine I got from the SxList:

[code];---------------------------------------------
; 7/02/04 PJM - This function uses a linear congruential
; sequence generator as a pseudo-random number generator.
RandomNumGen

;Rnew = Rold * 221 + 53
;221 = 256 - 32 - 4 + 1
;256 can be eliminated
;so we need to calculate Rnew = Rold * (1 - 32 - 4) + 53 using
;truncating arithmetic
;or Rnew = Rold * (-32 - 3) + 53

		clrb		C
		rl			RandomNum					;RandomNum' = 2*RandomNum and carry contains the original MSb
		mov			W, <>RandomNum       
		and			W, #$E0						;W = 16*RandomNum'=32*RandomNum
		rr			RandomNum					;restore RandomNum
		add			W, RandomNum               
		add			W, RandomNum
		add			RandomNum, W			;RandomNum'' = 32*RandomNum + 3*RandomNum
		not			RandomNum					;RandomNum''' = 255-RandomNum'' = -1 - RandomNum''
		mov			W, #54
		add			RandomNum, W			;RandomNum''''=-1 - 32*RandomNum - 3*RandomNum + 54
[/code]

"RandomNum" is a variable (in this case it's a global variable) that holds the value of most recent random number generated between interations.  Every time you call this routine, you'll update the value of "RandomNum".  If you want to find the original, search for "congruential" on the SxList site.  Make sure you go to the page with the SX code and not the PIC code.

[list]Thanks,
PeterM[/list]

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