No Subject

[jfox@xxxxxxxxxx (Jeff Fox)]

I forwarded two questions to Chuck from this mail list.

1. Xtal speed for PAL and source for info on the standards?

2. Xtal speed for refresh only on MuP21?

Here is Chuck's response: 

To: Jeff Fox > INTERNET:jfox@netcom.com

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You can't meet the PAL spec with the MuP21 video output.  That will
require a instruction to skip 1/4 a color period, whereas NTSC needs
to skip only 1/2.  However, you might be able to generate a displayable
signal.  For example, NTSC might work without interlace, depending
on the monitor?

My reference discusses PAL:
   Television Engineering Handbook
   K. Blair Benson
   McGraw Hill
   ISBN 0-07-004779-0
However, the relevant information is hard to extract.

The common PAL chrominance sub-carrier is 4.43 MHz.  The crystal
oscillator would have to be 4 times that.

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Figure on a refresh every 16 us.  That would be 64 KHz.  The refresh 
instruction occurs only every 4 instructions, for a clock rate of
256 KHz.  However, these refresh rates are enormously conservative.
I would try 32 KHz as a conveniently available part.

Another approach is a software refresh that promises to visit each page
each 16 ms.  You need only refresh the ones you use.