-----Original Message-----
From:   D Lloyd [SMTP:dan.lloyd@GB.ABB.COM]
Sent:   Tuesday, April 18, 2000 9:02 AM
To:     PICLIST@MITVMA.MIT.EDU
Subject:        Re: [OT] Software Random function

Marc <marc@AARGH.FRANKEN.DE>
17/04/2000 17:51




Please respond to pic microcontroller discussion list <PICLIST@MITVMA.MIT.EDU>

To:   PICLIST@MITVMA.MIT.EDU
cc:    (bcc: Dan Lloyd/GBPTD/ABB)
Subject:  Re: [OT] Software Random function

Security Level:?         Internal





>     LFSR:   RLF     RANDOM,W
>             RLF     RANDOM,W
>             BTFSC   RANDOM,4
>             XORLW   1
>             BTFSC   RANDOM,5
>             XORLW   1
>             BTFSC   RANDOM,3
>             XORLW   1
>             MOVWF   RANDOM
>             RETLW   0

Pretty predictable (short-term), isn't it?

* That's what I was thinkning. I imagine you have to be pretty careful how you
use this.

Dan

It's utterly predicatble.  It is after all, a PSEUDO random number generator.  It produces a repeating pattern of a very limited length.  Not sure if its 127 or 255 for this arrangement.  You could use a 24 bit (or more) register to get longer patterns though, using the same principle.  The Art of Electronics has a good section on maximal length PRBS generators.

Mike