KPURCELL@LIVERPOOL.AC.UK (07/27/90)
I mailed this to <bp@UUCP.pixar> sometime ago, but I think it bounced. I though it might be of general interest to the Z88 community, especially those in the US. I haven't tried this, but it seems that you can by static RAM modules with 256K and 512K byte capacity which fit in a single socket and has the 'standard' pinouts. If anybody tried it I'd like to hear from them. ---------------------------- message follows ------------------------------ I have been a z88 user for the past 4 years and it seems like a neat machine. I too have opened it up to have a look inside (not many chips!) and had a poke around. A similar upgrading Idea crossed my mind after eading an article in EPROM, the Z88 user group magazine (address below). My board is serial 005027 and is marked (just to right of VR1) "Z88 Iss 4" The info is as follows, from Z88 EPROM Sept/Oct 1988, vol 2, iss 5: ...the normal 64K address space is split into 4 16K pages. Withing any 16K section any one of 256 pages may be selected, thus the total memory space is a vast 4Mbytes. Which four pages are currently selected in the 64K address space is controlled by the opeating system, and it does this by writing to paging resigesters in custom chip. THe pages are splits as follows: 00-1f Internal rom (OZ) 512K max, 128k used 20-3f Internal RAM 512k max, 32k used 40-7f expansion slot 1 1024k max 80-bf expansion slot 2 1024k max c0-ff expansion slot 3 1024k max The first 32 pages are reserved for operating system and applications ROM. Only the first 8 are used [this leaves open the possiblity that you could cram a few more applications inside the machine by copying applications into a new bigger rom and replacing the current rom, which on my machine anyhow is socketed -kgp]. The next 32 are set aside for RAM, but only 2pages are used by the 32k fitted. I understand the circuit board will actually take a 128Kbyte chip -- perhaps the Z89 [this never happened, but why is beyond me, the added value is there for free. is there a bug in the os? -kgp]. (or even 256K -Ed [this comment must refer to the extra lines but it would make more sense to talk about 512K -- 32K times 16 -kgp]). The remaing 192 pages are spread acrossd the three slots allowing up 1o 1Mbyte each. ..the page selection registers are at I/O port address: &d0, &d1, &d2, &d3 and the OZ keeps a copy in the &400 page. Other points of interest on the pcb are: the Supercap capacitor next to the ROM (to allow the batteries to be changed with a reset) and the 21v inverter (for blowing the EPROMs) just to the left of the serial connector. All in all its a shame that they didn't socket the RAM chip, it would make an up grade a lot easier. To put a 128K ram in would probably need bad hack on the pcb to remove the current ram chip (with a risk of damaging the pcb). If you try it let me know! But it seems like a cheaper way to 128K machine. If nothing else you will get a bigger RAM:0 disk! The club address is: z88 users' club 68 Wellington street long eaton nottingham NG10 5NG UK There is a small program and some more info in the article I quoted above. Send me your postal address and I'll send you a xerox. [This is extended to anybody on the net!] Happy hacking, Kevin Kevin "fractal" Purcell | SURFACE SCIENCE CENTRE | The debugging of a one kpurcell@liverpool.ac.uk | Liverpool University | thousand line program Mac User Emotional Support | Liverpool L69 3BX | starts with a single step