[Coladam] Memory expander

John Turner gimechip at live.com
Wed Aug 8 04:13:22 CEST 2012


I actually laid out a 256K card using a 30 pin simm a couple of days ago. The only problem with 30 pin simms is that only the 8 and 9 chip 256k simms support 256-cycle refresh. All 30 pin simms above 256K and the 2 and 3 chip 256k require a 512 cycle refresh for proper operation. The Z80 provides a 7 bit (128 cycle refresh) and the MIOC provides an 8th bit for 256 cycle. This is Ras Only Refresh. If there were a convenient point to tap the !RFSH signal from the z80, you could probably use that to indicate to the SIMMs to do a CBR (cas-before-ras) refresh by swapping ras and cas at the simms during refresh time. It is something I have been pondering...
Headed off to work now...
I don't know if I'll actually build any of this stuff but I'll send the files to anyone who wants to play around with them...

Date: Tue, 7 Aug 2012 15:09:26 -0500
Subject: Re: [Coladam] Memory expander
From: oltmansg at gmail.com
To: gimechip at live.com

Sounds good! One of the zillions of projects I've had floating around in my head was a 30-pin SIMM RAM adapter card since 30-pin SIMMs are plentiful and you could do 1-4MB easily with one of those with a single SIMM socket (given enough bank addressing of course). I like your approach though since SRAMs in that size range are pretty cheap these days.


I'd like to see what you came up with for sure. Nice to see someone taking something from just a thought to a manufacturable product. ;)

I've decided to concentrate my efforts to fixing the couple of cards that I have now (the aforementioned PM IDE card and the unnamed 64/256K expander) and to work on a CP/M 3 BIOS. A documented/compilable BIOS would be nice to have to support new hardware since drivers could be integrated into it a little easier than what's currently out there.



On Tue, Aug 7, 2012 at 2:34 PM, John Turner <gimechip at live.com> wrote:



Geoff,

 I couldn't sleep when I got home this morning, so I looked in my parts box and found I had plenty of 128Kx8 Static RAMs and some ISP2032 CPLD's. I've put together a schematic and laid out a PCB for a 256K RAM card using three chips - the two 128Kx8 Static RAMs and one ISP2032 to handle the latching of the bank bits, etc. I think this should work. I have also implemented write protect either or both of the SRAMS may be write protected with a jumper. Also implemented is battery backup - I figured if I was going to use SRAMs (LP variety) then why not make it non-volatile. Anyway, it still needs and addressor or printer card to obtain the strobe signal to latch the bank byte. The bank byte provides address lines a16 and a17. a16 is used to decide whether to use the lower 64k or upper 64k of the sram and a17 selects which of the two srams are active. I've still got to do the cpld code, but a quick "schematic" entry in the lattice design software will take care of that. If you'd like to see the current schematic and board layout, I can email it to you when I get home from work in the morning (going to sleep now - this project has succeeded in eliminating my insomnia.) - John P.S. - The !CAS signal is used as the !CE of the active SRAM, !OE is tied active, and !WE functions as a R/!W signal (due to !oe tied active)...




Date: Wed, 1 Aug 2012 06:49:59 -0700

From: oltmansg at bellsouth.net

Subject: Re: [Coladam] Memory expander

To: gimechip at live.com; oltmansg at gmail.com; coladam at adamcon.org



John:



Yeah, even if you have the PAL, you'd still need an addresser card. I have an MIB3 so that's covered. I've never done PAL/GAL equations before, but I've got some existing stuff to use as a guide, so I'm sure I could come up with something. I just figured why reinvent the wheel if one already exists. ;)




I've got a dead PM IDE card too, with a blank GAL (was never programmed), so unless someone has those now too, that is on my to-do list as well.





From: John Turner <gimechip at live.com>

To: oltmansg at gmail.com; coladam at adamcon.org

Sent: Wed, August 1, 2012 1:40:12 AM

Subject: Re: [Coladam] Memory expander







Geoff - wouldn't you also need an addresser or printer card to access over 64K? If I remember correctly the 4464's support 256 cycle refresh same as the 4164 except that they are 4 bits wide - two would make 64k. I would therefore assume the PAL was used as the MUX chip. If the wiring differs from the MI card, then the MI PAL won't work. However, if you find yourself with some time, you could trace out the schematic with an ohmeter - I've done this with several old cards. What I do is draw a rough copy of the board and components. Then using multi-colored inks (to help me keep the wires separate) and and ohmeter, I recreate the board connections which then gives me the schematic. If you can generate a schematic, I am relatively certain I could write the proper GAL equations for you. - John




> From: oltmansg at gmail.com

> Date: Tue, 31 Jul 2012 22:13:16

 -0500

> To: coladam at adamcon.org

> Subject: [Coladam] Memory expander

>

> Hey guys, I have a memory expander with no silkscreen that is populated with 4464 DIP RAM and can (potentially) be expanded to 256k. I have no idea who made the thing, but I'd like to upgrade it. I have a feeling that it is a clone of the Micro Innovations card. This card has four jumpers on it, which I presume is used to select whether you're using it as a 64k card or a 256k one. On top of the missing 6 RAM chips, it is also missing a 7th chip, which I believe is a PAL/GAL (16V8?). Does anyone have any PAL equations or a dump of the PAL from the MI card? I'd like to max the sucker out.


>

> Also, anyone have a copy of a RAM tester program handy? I used to have one that would test up to 256k from the MI card, but I have no idea where this is now.

>

>



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