DIY RAM EXPANSION

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tcat
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DIY RAM EXPANSION

Postby tcat » Thu Mar 27, 2014 11:25 am

Dear All,

I have a plain 128k no TK2 good quality QL, I wish to expand it with a little amount of RAM, to get at least to a double i.e. 2x128k, as was the Sinclair option for QL developers back in 1984.

I am not much good at h/w designing as most of you here likely are. I looked at these components I wish to use to build my own expander ram.

DIN 2x32 1pc of female connector
DRAM 4164 a handfull
Some capacitors, resistors, not sure what values

Please see pictures.
DRAM 4164.JPG
memory

DIN 2x32.JPG
connector


I would welcome any guidence or suggestions of yours, as for where to get recommended PCB layout, is there an article in one of the QL USER back issues covering this, what other components I may need etc.

In the QL Technical Guide, there is a paragraph covering external peripherals and expansions, but I realise I need more advice to get started.

Many thanks in advance
TCAT


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1024MAK
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Re: DIY RAM EXPANSION

Postby 1024MAK » Thu Mar 27, 2014 11:37 am

I don't recommend using old type DRAM (dynamic RAM) chips for any new build. Old DRAM chips need some extra circuitry to generate the DRAM refresh signals. Given that static RAM (SRAM) chips of the sizes that are useful to us are now cheap, and are much easier to use, and need less "glue" logic, unless you want large amounts (>512k bytes) of RAM, use a SRAM chip.

Myself, I have been thinking of removing both Sinclair ROM chips, programming a EPROM with the OS & BASIC and putting this into one ROM socket. These leaves one ROM socket free to take a 128k SRAM chip. Of course, some extra chips will be needed to adjust the address decoding and for the DTACK signal.

This "project" has only got as far as the idea stage...

Mark


QL, Falcon, Atari 520STFM, Atari 1040STE, more PC's than I care to count and an assortment of 8 bit micros (Sinclair and Acorn)(nearly forgot the Psion's)
TabajaraLabs
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Re: DIY RAM EXPANSION

Postby TabajaraLabs » Thu Mar 27, 2014 11:53 am

I built one using a 512K SRAM chip and a PAL...Now where I found this design? I'll look for it and post here :)


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Re: DIY RAM EXPANSION

Postby Nasta » Thu Mar 27, 2014 12:36 pm

1024MAK wrote:I don't recommend using old type DRAM (dynamic RAM) chips for any new build. Old DRAM chips need some extra circuitry to generate the DRAM refresh signals. Given that static RAM (SRAM) chips of the sizes that are useful to us are now cheap, and are much easier to use, and need less "glue" logic, unless you want large amounts (>512k bytes) of RAM, use a SRAM chip.

Myself, I have been thinking of removing both Sinclair ROM chips, programming a EPROM with the OS & BASIC and putting this into one ROM socket. These leaves one ROM socket free to take a 128k SRAM chip. Of course, some extra chips will be needed to adjust the address decoding and for the DTACK signal.

This "project" has only got as far as the idea stage...

Mark


DRAM is not trivial to interface, and using old DRAM is really not recommended. Besides, 16 chips are needed for 128k, the board and sockets will cost more than buying a single 512k SRAM chip which is nearly trivial to interface to the bus.

The QL ROM socket has 28 pins and a total of 16 address lines, hence you can put at most 64k SRAM into it, and that's assuming you use wires to get to the rest of the address lines, read/write, data strobe, DSMCL etc...


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Dave
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Re: DIY RAM EXPANSION

Postby Dave » Thu Mar 27, 2014 5:40 pm

The one thing people ask for most is a simple floppy interface and 512K RAM. There isn't room in the market to do both UltraQ and the basic interface, so I won't be doing it unfortunately, but there is a good chance I will do a basic 512K expansion by itself that can replace a lot of older memory expansions, be a bit quicker, and use a lot less power... I've been fence-sitting on that one for a long time.

Haven't decided if I should get off the fence or not.


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Mr_Navigator
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Re: DIY RAM EXPANSION

Postby Mr_Navigator » Thu Mar 27, 2014 6:04 pm

Dave wrote:The one thing people ask for most is a simple floppy interface and 512K RAM. There isn't room in the market to do both UltraQ and the basic interface, so I won't be doing it unfortunately, but there is a good chance I will do a basic 512K expansion by itself that can replace a lot of older memory expansions, be a bit quicker, and use a lot less power... I've been fence-sitting on that one for a long time.

Haven't decided if I should get off the fence or not.


Do I detect a crack developing in your nether regions after all this fence sitting?


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Derek_Stewart
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Re: DIY RAM EXPANSION

Postby Derek_Stewart » Thu Mar 27, 2014 6:12 pm

Hi,

I could not read the comment in yellow, as I get the QL Forum by RSS feed.

Only when I selected the message and Thunderbird with ThunderBrow Addon opened the web page, could I read the comment. :P

Derek


Regards,

Derek
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Mr_Navigator
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Re: DIY RAM EXPANSION

Postby Mr_Navigator » Thu Mar 27, 2014 6:14 pm

Derek_Stewart wrote:Hi,

I could not read the comment in yellow, as I get the QL Forum by RSS feed.

Only when I selected the message and Thunderbird with ThunderBrow Addon opened the web page, could I read the comment. :P

Derek


I will consider that for the future Derek :)


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tcat
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Re: DIY RAM EXPANSION

Postby tcat » Thu Mar 27, 2014 6:23 pm

1024MAK wrote:I don't recommend using old type DRAM (dynamic RAM) chips for any new build. Old DRAM chips need some extra circuitry to generate the DRAM refresh signals. Given that static RAM (SRAM) chips of the sizes that are useful to us are now cheap, and are much easier to use, and need less "glue" logic,

Mark


Cannot the QL internal qlue and line addressing be somehow reused through expander connector, providing it similar RAM chips to those used inside QL, though fitted on a separate board?

I have seen this SIMPLEX RAM Expansion here
http://www.rwapadventures.com/ql_wiki/i ... on&lang=en

TCAT


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Re: DIY RAM EXPANSION

Postby Brane2 » Thu Apr 03, 2014 1:38 am

Don't mess around with DRAM chips, especially that old ones.

If you know what you are doing, you might be able to cobble up the expansion with a couple of PC's old DIMM modules. YOu could put in 680008 in PLCC so you could use 4M adress range.

This should be simple, since practically all CPU signals are already on expansion connector.

But there is much simpler way.

I'm just plwoing through Digikey and there are plenty of cheap SRAMs that could do the job nicely, without much complication. If you pick Asynchronous SRAM's in 4Mbit or 8Mbit categories that work work 5V, you'l get plenty of chips for under $10.

I am looking at Alliance Memory "AS6C8008-55ZIN", for example. 8 Mbit SRAM ( =1M x 8 bit) that works at 2.7V-5.5V in 32pin SOIC. Speed: 55ns Price: $5.6/pc

Connecting this to QL could be so simple that you wouldn't even need PCB if you are a bit of a hacker.


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