Re: Blurry picture

From: Gerrit Heitsch <>
Date: Tue, 15 Nov 2011 18:28:00 +0100
Message-ID: <>
On 11/15/2011 03:47 AM, Segher Boessenkool wrote:
>>> Sorry for the mistake. I think that may have been an earlier design I
>>> was remembering from Al Charpentier's notes about having to add a PLL
>>> to keep them in sync.
>> That was the VIC-II and all its derivates. In the end the decision to
>> supply dot clock and color clock to the VIC-II independantly resulted
>> in the need for the PLL and in the end gave us the little MOS 8701.
>> Even though MOS reworked the VIC for the C128, the 8701 is still
>> present there.
> The MAX machine used dual crystal oscillators (in discrete parts).

The first C64 board had a layout that suggested that they had planned 
the same there:

I read somewhere that 2 crystals resulted in poor picture quality 
compared to using a PLL and only one crystal. Never understood why.

> I don't think it would have been possible to make an 8701 in the
> older 65xx NMOS process, 36MHz is too much.

I'm surprised they were able to get 36MHz working with HMOS-II.

> Are there die photos of the VIC-IIe somewhere? It would be interesting
> to see what changed on there (what exactly changed functionally, anyway?)

The VIC-IIe still uses the 8701, so the clock part didn't change.

Otherwise it got a few I/O-Bits and the ability to switch the CPU clock 
between 1 and 2 MHz. More details can be found here:

Looks like there were some extra 'undocumented' features added as well


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Received on 2011-11-15 18:00:04

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