Re: 250466 PCB curiousness

From: Pasi Lassila <pasi.lassila_at_gmail.com>
Date: Sun, 7 Jul 2019 23:24:39 +0300
Message-ID: <CACM8tfDB9twrV36ebtZs=CB_pga-VdEaFBgY8dgL_xgOV=DjEg_at_mail.gmail.com>
You can mix address pins together and data pins together and the RAM works
the same. Some manufacturers don't even number the address or data pins
since you can freely mix them.

I made an SRAM board recently. I have it for sale at FB, Amibay and Lemon64.
http://www.amibay.com/showthread.php?106896-SRAM-for-C64&p=945376#post945376

During layout I enabled pin swap for the pins and this allowed for an
easier layout.

I also noticed Commodore swapped some pins.

-Pasi

On Sun, Jul 7, 2019, 10:46 PM Jim Brain <brain_at_jbrain.com> wrote:

> Memory in a 250466 PCB went flaky, so I tried my hand at repair.  The PCB
> is the 3 ROM version, but with 4164 DRAMs.  After desoldering the DRAMs,
> socketing, and installing some new DRAMs (all working now), I decided to
> see if I could switch the unit over to SRAM.  It appears I and some other
> folks had similar ideas, as I see another project on Facebook to convert as
> well.  I went a different direction and leveraged a small CPLD to do the
> conversion.  After fighting last night with unsoldered pins, it is now
> working.
>
> I decided to play around with the unit and map out the address pins.
> Interestingly, I find that MA6 and MA0 appear to be swapped on the PCB.  I
> verified that MA6 indeed goes to MA0 on the 6567, though without a
> schematic, it's hard to trace MA6 (it goes through a '257, etc.).  Anyone
> have a schematic? (Zimmers does not appear to have one) And, does anyone
> know if pin swapping was done on other versions?
>
>
> --
> Jim Brainbrain_at_jbrain.com www.jbrain.com
>
>
Received on 2020-05-29 21:48:47

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