Re: PET with 8MHz :-)

From: Nate Lawson <>
Date: Sun, 03 Jan 2010 10:17:08 -0800
Message-ID: <>
André Fachat wrote:
>> Since IEEE-488 is dependent upon hand shaking it should work fine.
> Yes, IEEE488 relies on handshaking and the VIA whose timer is used for timeout is still clocked at 1MHz.
> However, I had already experimented with a 2Mhz PET version (clocking my selfbuilt computer with a Fat40 ROM at 2MHz) but it did not work (even though I modified the timeout values).

It could be a problem in the clock domain crossing from the CPU to the
6522 VIA. Is it a single clock divided /8 or is it multiple clocks?
Also, are the setup and hold times preserved when crossing this boundary?

> Now the three alternatives I have: 
> 1) fix my lpt-ieee488 interface - a mess of wires on breadboard...
> 2) simply us a real 4040 or 8250 drive which would involve taking the drives down from the attic
> 3) build an ATMEL based lpt-ieee488 replacement, using USB instead of the printer port...

XS-1541 already supports IEEE-488 or you can take the XUM1541 design and
hack in the IEEE-488 code from XS-1541.


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Received on 2010-01-03 19:00:04

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