RAM at 8-12, EEProm at 12-16k

Any discussions related to the creation of new hardware or software for the ZX80 or ZX81
sirmorris
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RAM at 8-12, EEProm at 12-16k

Post by sirmorris »

I'd like to make a board like this.

Anyone done anything similar?

Cheers!
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Andy Rea
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Re: RAM at 8-12, EEProm at 12-16k

Post by Andy Rea »

Decoding using 2 chips, use 2732 and 2 off 6116 or similar. just knocked it up off the top of my head...(spotted 1 mistake already need a signal diode between the edge connectors /ROMCS and the output of the INVERTER !) rush rush rush.....

http://i243.photobucket.com/albums/ff60 ... romram.jpg

regards Andy

P.S. what Ram chip did you want to use ? could be done differently for different ram chips.
AFK
sirmorris
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Re: RAM at 8-12, EEProm at 12-16k

Post by sirmorris »

Nice!

I was thinking on my cycle ride home (in the rain) about a 'zeddie simulator'.

This week I've been trying to program some eeproms that I've pulled from some old PC motherboards - 29ee010/020 units. I've hooked them up to an arduino and an i2c I/O expander and tried to read from them. I'm getting really funky results and I want now just to hook it up to a 'proper' address/data bus and see if it works any better. Now then i thought - I'll put it on a zeddie! Hmm - but I need decode logic - and - well, that's just a _tiny_ bit beyond me. But what if I had a way of simulating it?

Well that got me to thinking - Arduino driving a pair of Max6965 i2c IO expanders into an edge connector. A zeddie simulator. You could effectively 'script' the changes in the signal lines and watch the results on the prototype logic you've dangled off it. Are you with me so far?

Arduino (or similar) -> IO expanders -> Edge connector -> ... >--Prototype board.

The thing about this is that you don't need a big fat wide logic analyzer or oscilloscope. You could clock the 'fake zeddy' real slow and probe the prototype logic at your leisure :)

Is that a good idea or is it the merlot talkin'?!

I thought about writing this in software. That's a bigger picture though.

C
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Andy Rea
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Re: RAM at 8-12, EEProm at 12-16k

Post by Andy Rea »

LOL i'm such a dummy ! never even considered /MemReq or /Refresh !

Going bed to get some rest and will draw better hopefully correct circuit tommorow :lol:

Andy
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sirmorris
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Re: RAM at 8-12, EEProm at 12-16k

Post by sirmorris »

Forget /refresh - static ram only please!

Andy - please see new subject in enulators topic about hardware simulator. It might be up your street.
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Andy Rea
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Re: RAM at 8-12, EEProm at 12-16k

Post by Andy Rea »

Okay dokay

here is 1 chip version ! uses a few other components as well,

Regards Andy
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sirmorris
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Re: RAM at 8-12, EEProm at 12-16k

Post by sirmorris »

Gorgeous!

I love the transistor-inverter!
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siggi
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Re: RAM at 8-12, EEProm at 12-16k

Post by siggi »

/MREQ should be used to enable the 138. Otherwise there could be some glitches, while the address lines are setup. So I would swap /MREQ and A15.

Siggi
My ZX81 web-server: online since 2007, currently offline due to hardware problems
http://zx81-siggi.endoftheinternet.org/index.html
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Andy Rea
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Re: RAM at 8-12, EEProm at 12-16k

Post by Andy Rea »

Good Point.

Thanks Siggi

Regards Andy
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sirmorris
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Re: RAM at 8-12, EEProm at 12-16k

Post by sirmorris »

It's fair enough that we assume ram = ~rom, but I don't understand the actions of the transistor. It's operating on both the newram and newromcs lines at the same time?

:?

C
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