[Coco] [Color Computer] Re: POKE 65495,0

[Darren A.]

>From: jdaggett at gate.net
>
>There was a second generation of the SAM chip called 74LS785 that I think 
>appeared in the
>Coco2. One of its main features was to extend the refresh counter from 7 
>bits to 8 bits. This
>allowed the usage of 64Kx1 dram chips. Since I don't have a spec sheet on 
>the 74LS785, so
>I can't verify that any other functions have changed. From what I have read 
>the 74LS785 is
>pin for pin compatible with the 74LS783/MC6883.
>
>james
>
>--

As far as the FAST mode issue is concerned, the datashet for the 74LS785 
indicates that its bahavior is identical to the 74LS783/MC6883. 
Specifically, it states that both RAM refresh and VDG access are not 
provided in FAST mode.

It describes the differences from the 6883 as:

The SN74LS785 has been modified to support 16K x 4 and 64K x 1 (256 column 
refresh) dynamic RAMs. A further enhancement allows for the LS785 to support 
low power dynamic ROMs (such as MCM68364) without additional logic.

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