Re: cbm 8032 motherboard + 4164

From: Gerrit Heitsch <>
Date: Fri, 14 Oct 2016 13:01:43 +0200
Message-ID: <>
On 10/14/2016 12:48 PM, smf wrote:
> On 14/10/2016 11:35, Gerrit Heitsch wrote:
>> And don't forget, the DRAM controller came later, the 6566 was SRAM,
>> so it had to fit into whatever space they could find. That also
>> explains the weird multiplex address pinout.
> I need to track down who told me they had a decap of the 6566 and it
> looked like it was based on the dram design with traces cut. VIC2 was
> originally destined for a dram system, circumstances meant the 6566 was
> first out of the gate & that the p500 (the target machine) never went
> into full scale production.

Well, MOS usually counted upwards so the number suggests that the 6566 
came first.

> 6567 do multiplexed for dram and non-multiplexed for character rom, I
> would guess that has just as much to do with any weird pinout.

TED is completly non-multiplexed. It's likely the number of pins they 
had and non-multiplexed just didn't fit into a 40pin.

The VIC in the VIC-20 was SRAM and had the same address space and 12 
data bits. The problem is, for DRAM you also need /RAS and /CAS which 
means 2 more pins. Going to multiplexed addresses solves that problem. 
But then you need to demultiplex for the char ROM. The easiest way to 
solve that is to have some non-multiplexed addresses and the 74LS373 as 
used in the C64.


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Received on 2016-10-14 11:03:14

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