Re: Early TED/Plus4/C116 Schematics

From: Gerrit Heitsch <>
Date: Sat, 07 Sep 2013 18:09:54 +0200
Message-ID: <>
On 09/07/2013 04:43 AM, Bil Herd wrote:
> 30 year old schematics for early TED.  Will probably have better contrast on
> the greyscales tomorrow.

Neat... I also noticed the circuit for the disabling the internal RAM by 
pulling the _G pin of the TMS4416 high.

This of course would still make write cycles reach the RAM since _G only 
disables the output. It would have been useful for external memory 
expansions, but not for anything that only temporarily disables the 
internal RAM. That would have needed a circuit to gate _CAS.

As for your note about R/_W and driving it. VIC in the C64 doesn't drive 
it so once the 6510 is taken off the bus with AEC low, there is only a 
pullup on R/_w which doesn't give a sharp edge but a rather slow climb, 
kind of ugly, but works. The TED datasheet I have states that TED will 
drive R/_W HIGH in his part of the cycle, so I assume that there was 
another chip revision to add this little detail to TED?

I assume that the chip engineers didn't think about it due to VIC.


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Received on 2013-09-07 17:00:13

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