Simple 8-16K RAM Mod Question

[Slipstreem]

Thanks, Vincent. This is mostly a 'bits from the spares box' project, plus I'm planning on fitting much more besides the 8-16K RAM upgrade inside a standard ZX81 case, so it's a matter of keeping the parts count down as much as sensibly possible, even if that does involve making the odd sacrifice in terms of hardware flexibility. I won't tell you what else is going inside just yet incase it all goes horribly wrong, but I'll start a fresh thread with a full list of upgrades and some photos as soon as it's finished.

[Andy Rea]

Sounds interesting, go on spill the beans, probably someone here has been there and done that already so may be able to offer advice

Andy

[VinCBR900]

Intel 8231?

http://shop.ebay.co.uk/i.html?LH_PrefLo ... intel+8231

[Andy Rea]

Intel 8231?

That would be wicked... Anybody clever enough to patch the zx81 rom to use it

Andy

[siggi]

Thanks, Vincent. This is mostly a 'bits from the spares box' project, plus I'm planning on fitting much more besides the 8-16K RAM upgrade inside a standard ZX81 case, so it's a matter of keeping the parts count down as much as sensibly possible, even if that does involve making the odd sacrifice in terms of hardware flexibility.)

Well, I squeezed 2x32 KB Ram (from 0..64K), 32 KB EEPROM (2 Banks from 0..16K), a MMC- and an USB-Interface into a standard ZX81 and built my ZX81 Laptop (with LCD-Display-"TV"). And it works ...

P1020684_1024x768.JPG (212.69 KiB) Viewed 3897 times

Siggi

PS. In Tom's Forum http://forum.tlienhard.com/phpBB3/ a thread describes all details on my Zeddy-Laptop (but it is only accessible for registered users: http://forum.tlienhard.com/phpBB3/viewt ... =305#p1642).

[Slipstreem]

Very nice! I'm not going for anything quite that elaborate, but I'm impressed!

If all goes well, mine should end up with 40KB of internal RAM with the top 16KB battery backed, a buffered composite video phono output replacing the UHF TV phono output, stereo sound with a modified version of Wilf Ritger's ZONX clone with internal speakers and phono outputs, a 3.5" LCD screen mounted in the case lid, and a modified EAR socket input circuit that'll listen to an el-cheapo MP3 player for quick loading of files generated with OTLA 2.2. It may also 'grow' an internal rechargeable battery pack chunky enough to run the whole unit for a few hours to make it a truly portable device, space permitting.

I've already swapped out the original Z80 CPU for a CMOS version and the original 1KB of RAM for 32KB, and the current consumption has dropped from 420mA to 230mA, so even with the remaining goodies to go in there, decent battery life shouldn't be too hard to achieve. All the other bits I need are either here already or on order.

I'll let you know how it goes.