[sdiy] SRAM like 5101

[ChristianH]

On Thu, 11 Apr 2002 18:20:58 +0200 (MEST) Rainer Buchty wrote:

> 
> > In that case it's probably better to do a redesign, in order to use
> > something like 6116s (2kx8). Of course it will depend on the surrounding
> > circuit if this is easily feasible. IMHO, adding a couple of 'LS245
> > 3state buffers would be better than relying on obsolete parts, but gate
> > timing may require some thinking.
> 
> I don't think that timing would really be an issue since the 5101 has
> 650ns access time according to Chipdir (can you say "slow"?);

Access timing surely wouldn't be an issue here. I meant 'LS245 (or
similar) direction and gate timing - the buffer will have to gate input
data to the (common I/O) RAM, providing sufficient setup&hold times
before&after the RAM write pulse. Maybe we could use an analog pulse
shaper. Any analog gurus in here...?

> But... Does the PS3200 really access in and out data buses separately or
> are these buses merged to a common data bus anyway which then is accessed
> by a CPU or some simple control logic? In that case it might be easier to
> tap the common data bus.

I don't have any PS schematics, but I'd expect the memory to be wired
similarly to the Trident: ADC output into RAM DI, and RAM DO into DAC.
And some adventurous counter scheme for addressing.
I'm not even sure if there's a CPU at all in the PS's. Possibly a cute
one for KB scanning.

cu
Christian