Thanks a lot for the explanation.

The problem is that I can not afford to call the routine 8 times:
I can only afford to call the routine at most two times.

I am doing this on a 12F629 with 4MHz internal oscillator (1us per
instruction) and my normal loop time can not exceed 125us (with a
filter depth of 8, which lead to 1ms response time for the program).
The fixed loop time is about 70us and I want to generate a delay of
24-52us (20us overhead + 4-32 us of delay) leading to a loop 
time of 94-122us ( average 108us). So I have very limited 
time to do this.

Regards,
Xiaofan

-----Original Message-----
From: Wouter van Ooijen [mailto:wouter@voti.nl]
Sent: Thursday, June 23, 2005 7:25 PM
To: 'Microcontroller discussion list - Public.'
Subject: RE: [PIC] Simple pseudo random code generation

It does. Each time you call this routine it shifts the (in this case
16-bit) value on step and generates one new pseudo-random bit, which is
inserted into the just vacated bit. If you want it to generate for
instance a random byte you must call it 8 times, otherwise there will be
a very strong correlation between successive bytes.

OMHO 16 bit is often a bit short, I would opt for a 24-bit SR.

...
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