Re: Hardware-based vs software-based emulation

From: Gerrit Heitsch <>
Date: Tue, 21 Feb 2017 16:11:24 +0100
Message-ID: <>
On 02/21/2017 09:12 AM, Francesco Messineo wrote:
> On Tue, Feb 21, 2017 at 8:32 AM, Baltissen, GJPAA (Ruud)
> <> wrote:
>> Hallo Gerrit,
>>> When I did my experiments with SRAM to replace the DRAM in a C64 it was never really stable until I added the OR gate to the circuit.
>> Have you documented this anywhere, including schematics?
> I have not tried it, but I assume it should be easy:
> 74LS373 (or 573) latching the 8 row address lines from original DRAM
> to the first 8 address lines of SRAM chip, /OE tied low, LE driven
> directly by /RAS. Direct connection between the 8 original DRAM
> address lines to the other 8 address lines of the SRAM (old column
> address). /CE of the SRAM = /RAS OR /CAS. R/W signal should go
> directly.
> Correct me if I'm missing something.

No, that's the circuit I used. I used a '573 since that one has a better 
pinout, you can place the Latch and the RAM side by side and save having 
to wire 8 lines. Also, I didn't observe the address line numbering on 
the RAM (A0 to A0, A1 to A1...). It's a static RAM, so you can connect 
the address lines in any order you like. Same for the data lines.

The idea for the circuit came from the way the address signals for 
char-ROM and color-RAM are generated in the C64.


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Received on 2017-02-21 16:00:02

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