[sdiy] Homemade Memorymoog - update
luis.marka at terra.com.br
Mon Feb 18 18:17:40 CET 2019
I just linked to a part of the schematics because, well, they are huge!
I can provide the full page board diagram if you want to take a look,
just let me know.
On 17/02/2019 22:36, MTG wrote:
> The 27128 *maybe*. It's 4x the size of a 2732 and 1/4 of that seems to
> leave your schematic via a signal called ROM*. Need to figure out
> what that is. See pin 12 on U9
The ROM signal out of U9 goes to a 40 pin connector that was made
available for future expansion: sequencer/MIDI boards, etc. I am keeping
this connector in the current board clone, but will get rid of it in the
compact version I am working on, have no plans to implement the
sequencer. Now, if I got it right, U9 will be gone and the OE pin in the
27C128 (pin 22) will receive its signal directly from pin 1 in U12... is
that correct, or am I missing some detail here?
> The SRAM you are OK with near as I can tell. You could use an Alliance
> 6264 from Mouser. That logic is butt-ugly though. I'm not sure how
> much you can really clean it up without a total redo. There are four
> off-page RAM signals, looks like another 8k x 8. Where do those go out
> of curiosity?
Those are data and address bus, plus RD and WR from the Z80 that are
used by the DMUX and keyboard/panel scan circuits.
The Memorymoog implements a mechanism to protect data RAM chips at
shutdown: it taps voltage directly from the rectifiers in the power
supply, before the filter capacitor. At shutdown, voltage in this line
drops a few milliseconds before the voltage in the main power bus due to
capacitance. The "power shutdown" circuit then feeds a low signal to
U22, which in turn disables the RAM chips before power is gone (hopefuly).
Still doing my homework on how to address the RAM chip should I go for
one single SRAM IC, I have not touched this type of circuit since the
> I don't suppose there is a new Z80 that's flashed based with some of
> those peripherals inside? It seems on the 8051's got lucky that way.
> I would glance at the Kiwi Technics stuff and Tauntek (sp?) to see if
> there are clever subs for the Z80.
> On 2/17/2019 3:55 PM, Luís Marka wrote:
>> Short update: got the digital board pretty much done, here:
>> Not as compact as I thought it would be, but was a good training in
>> using Kicad. Now ordering the parts, and making the final revision
>> before sending the board for fabrication.
>> Already started work on a more compact version of this board: SMD for
>> some of the components, getting rid of the sequencer connector and
>> replacing 3x 2532 EPROMS (already changed for the 2732 in my board,
>> had a number of 2732 around and I already did manage to burn the
>> firmware on those, so why not?) with one single 27C128. In the same
>> line, would it be possible to replace the 4x 2k 6116 SRAMs with 1x 8k
>> AS6C6264, for example? For reference, the Memorymoog memory control
>> section is here: https://imgur.com/a/fnsf1qs
>> Any help in implementing the logic for this reduced number of memory
>> chips is much appreciated! In the mean time, will attack the PSU and
>> DMUX boards.
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