Re: Hardware-based vs software-based emulation

On 02/21/2017 09:56 PM, smf wrote:
> This thread has a schematic
>
> http://www.lemon64.com/forum/viewtopic.php?t=56301&postdays=0&postorder=asc&start=15
>
>
> It looks like he did alot of testing and had to change a few things each
> time he hit a problem.

Yes... And he still uses /CASRAM as /CS without OR with /RAS. That is 
not stable, he can only get away with it since he uses such a slow RAM 
(100ns), but it's not guaranteed to work in all instances and PLA versions.

Also, I don't quite understand what he was doing with the diodes and 
using anything but plain MA0-MA7. If you use those, you can make a plug 
in module for the RAM without needing any other signals (despite what 
was being said in the thread)

  Gerrit




>
>
> On 21/02/2017 15:11, Gerrit Heitsch wrote:
>> On 02/21/2017 09:12 AM, Francesco Messineo wrote:
>>> On Tue, Feb 21, 2017 at 8:32 AM, Baltissen, GJPAA (Ruud)
>>> <ruud.baltissen@apg.nl> 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.
>>
>>  Gerrit
>>
>>
>>
>>       Message was sent through the cbm-hackers mailing list
>
>
>       Message was sent through the cbm-hackers mailing list
>
>


       Message was sent through the cbm-hackers mailing list