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Author Topic: Internal memory expansion (Read 51174 times)

Offline Saint

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Re: Internal memory expansion
« Reply #90 on: 2013.October.22. 11:06:28 »
Quote from: Zozosoft
I hope it is will be enought fast for 10MHz Z80!
Easily, yes. :) 10Mhz is 100ns cycles, so I think you could run over 20Mhz with this SRAM, probably much more given the Z80 memory access cycles.

Are you replacing the internal RAM also? Or is that just slow access anyway as it's through the Nick?

Offline Zozosoft

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Re: Internal memory expansion
« Reply #91 on: 2013.October.22. 11:12:29 »
Quote from: Saint
Easily, yes. :) 10Mhz is 100ns cycles, so I think you could run over 20Mhz with this SRAM, probably much more given the Z80 memory access cycles.
Great!

Quote
Are you replacing the internal RAM also? Or is that just slow access anyway as it's through the Nick?
Not needed because the CPU access also controled by the Nick, with fixed timing.
I tested with 10Mhz some motherboards, not problem with the video memory. But the old slow DRAM expansions not working at this turbo speed.
« Last Edit: 2013.October.22. 12:57:24 by Zozosoft »

Offline lgb

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Re: Internal memory expansion
« Reply #92 on: 2013.October.22. 11:46:31 »
Quote from: Saint
Yes, I agree. The SRAM is actually 55ns, so it is running way below it's maximum frequency, and will be drawing more current while switching. So it should be running cool compared to what it can do.

Also an important factor: I don't know your design too much, but modern CMOS SRAM memories go into low-power mode if chip select is inactive. Some can create a design that CS (or CE, it seems there are different habits to name this kind of pin on ICs) is always active, tied to GND (since it's a low-active signal) and only OE and WE is used to control RD/WR operations. However in this design causes not allow SRAM to go into low-power mode when it's not needed. A typical value is like 10uA only when not selected, but eg 10mA if it is, and even higher like 50mA or so when an operation is done. At the other hand, I was told many years ago that at quite rapid access it's better idea (even with the cost to increasing heat and current) to keep IC always selected since near its specification, it can be faster to have stable address signals already when OE or WE happens actually. If CE is activated only at the same time, maybe you can't reach the full speed of the memory. However since I guess it's far from its limit, it's better not to hard-wire CS as selected all the time. Sorry if I write too trivial stuffs, honestly I have limited experience, and much more 'by theory' stuff :) Also I don't know your implementation, and the GAL internals how you create SRAM signals after all.

Offline Zozosoft

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Re: Internal memory expansion
« Reply #93 on: 2013.October.22. 22:14:31 »
Quote from: Saint
Yes, if you would like to find out how many 1MB / 512KB versions people would like, I will try and got those built.
Currently: 7x1M, 3x512K, another one waiting for answer
« Last Edit: 2013.October.22. 23:51:05 by Zozosoft »

Offline Saint

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Re: Internal memory expansion
« Reply #94 on: 2013.October.22. 22:50:48 »
I have written up a simple how-to for installing the RAM expansion!

http://www.retrohq.co.uk/Installation.html

Bagpuss22 has received his today, so I hope we'll have the first upgraded Enterprise soon. :)

Offline Saint

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Re: Internal memory expansion
« Reply #95 on: 2013.October.22. 23:02:20 »
Quote from: lgb
Also an important factor: I don't know your design too much, but modern CMOS SRAM memories go into low-power mode if chip select is inactive. Some can create a design that CS (or CE, it seems there are different habits to name this kind of pin on ICs) is always active, tied to GND (since it's a low-active signal) and only OE and WE is used to control RD/WR operations. 
In the case of the Alliance SRAM I am using, it has /OE, /WE and /CE. I simply connect /RD to /OE, /WR to /WE and then the address decoding output to /CE. So as long as the memory is not being accessed, the chip is not enabled. If there is any power saving, then the chip will power down properly. :)

Offline Bagpuss22

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Re: Internal memory expansion
« Reply #96 on: 2013.October.23. 20:11:10 »
Well I have installed both EXOS 2.4beta AND 512K!!

512K did not register at first, but a wiggle later and all is well...... 
APART from then my original keyboard membrane has now given up!!! (new one ordered :smt023)


The inner sanctum!




Loads of memory!!!!

Thank you JAMES! :shock:

BP22

Offline Z80System

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Re: Internal memory expansion
« Reply #97 on: 2013.October.23. 20:28:24 »
In this photo I can see the sizes better.

It is so tiny, it is so little, it is so cool.

When will the SD card + memory combo be ready ? :)

Is it not possible to work an IDE controller (like Zozo's one)+ IDE to SD + SD card alltogether to a cartridge ? RAM expansion will be in this new form, and SD card goes to a cartridge ?

If it would communicate through IDE, then the softwares nearly ready, because EXOS handles that. As far as I know ...

And in a cartridge, we could replace the SD card, when it has no wifi. We will not place the only screw to the cartridge, and we can split the cartridge easily to replace the SD card.
Z80 System

Offline Saint

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Re: Internal memory expansion
« Reply #98 on: 2013.October.23. 23:15:29 »
Superb! Great to see it working outside of my Enterprise. :ds_icon_cheesygrin: Odd you should have connection problems, though -- I've not had even one problem throughout testing the units, they have all just worked perfectly first time!

The keyboard membranes are a nightmare. I unplug and replug mine so regularly, it's going to stop working soon... :shock:

Z80System:
Yes, it is a very tiny PCB! I had to rework the PCB layout a couple of times to get it so small, and it halved the price of the PCB manufacture getting it down under 5x5cm.

I have plans to 3D print a new cartridge for the SD card interface with a slot in the end for removing the SD card, or failing that I have some edge connectors for an expansion port version. I have had quotes already for the 3D printing, and it doesn't seem impossible. But equally I have ideas to make an internal SD card + memory expansion, just because I think it would be cool to have an internal "hard drive" in the Enterprise... :ds_icon_cheesygrin: It would replace the existing memory expansion with the same connectors.

And a quick update: I have received my new order of SRAM chips today and have written new GAL logic for the 1MB expansion board, so I will try the 1MB board next.

Offline Bagpuss22

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Re: Internal memory expansion
« Reply #99 on: 2013.October.24. 10:12:28 »
@Saint

The new keyboard membranes are VERY good quality, and are much better than the originals.

They are made of slightly thicker plastic and so will last longer.  I have upgraded both my machines
now and even sent some to Zozo.

Russ

Offline Saint

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Re: Internal memory expansion
« Reply #100 on: 2013.October.24. 10:27:04 »
Quote from: Bagpuss22
@Saint

The new keyboard membranes are VERY good quality, and are much better than the originals.

They are made of slightly thicker plastic and so will last longer.  I have upgraded both my machines
now and even sent some to Zozo.

Russ
I've been thinking about getting some, for when mine do eventually die! I will probably take the plunge with the bit of cash I'm getting from the RAM expansions... only seems right. :razz:

Good to hear they are nice quality!

Offline Z80System

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Re: Internal memory expansion
« Reply #101 on: 2013.October.24. 11:29:40 »
Quote
But equally I have ideas to make an internal SD card + memory expansion, just because I think it would be cool to have an internal "hard drive" in the Enterprise...  It would replace the existing memory expansion with the same connectors.

Yes, it is a very very cool idea too ... and with those wifi SD cards, the main problem is solved (accessing the SD from outside of the EP), even if there will not be other EP supported way to access it.

So I think everyone just cannot wait for it ... :)
Z80 System

Offline Saint

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Re: Internal memory expansion
« Reply #102 on: 2013.October.24. 22:10:46 »
Zozo: I've tried the 1MB expansion, and have a working prototype, but it takes me too long to solder on the piggyback chip. It's quite awkward as my hands are not very steady, and the result is quite messy. So I'm afraid I will only be offering the 512KB expansion for the moment. :(

So if you could check for me how many 512KB expansions are wanted from Hungary, I'll build up the remaining boards I have for 512KB.

Once I've done the SD card interface I may look at making a "mega" memory expansion which will accept up to 4MB (8 chips) and decode everything but the cartridge and EXOS memory pages if enough people are interested! It would use the same connectors, and you could also re-use the socketed SRAM from the 512KB board.

Offline Zozosoft

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Re: Internal memory expansion
« Reply #103 on: 2013.October.24. 22:22:48 »
Send the components and I will assemble it!

Offline fatbob_gb

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Re: Internal memory expansion
« Reply #104 on: 2013.October.24. 22:41:40 »
My newly installed memory expansion (and EXOS 2.4beta) is working perfectly :ds_icon_cheesygrin:

Sadly another Enterprise membrane gave up the ghost though, luckily I had a spare one handy, better get another one ordered.

Thanks James & Zozosoft also for the updated EXOS.
« Last Edit: 2013.October.25. 11:59:16 by szipucsu, Reason: Correcting the emoticon visuality »