") (07/24/89)
Well, I am a currently enrolled student living in the college-provided
housing (a.k.a. Dorms). It so happened that I had to move almost every
semester and go home to Korea over the summer, which means that having
databooks that fill a 4-by-six space was a drag, which lead me to "weed
out" duplicate and "obsolete" copies. I knew I shouldn't have, but
the "friends (like the recent popular music proclaims)" forced me to.
I say, never trust your "friends!" I just realized that most companies have
decided to cut back (or discontinue) on their 64-k DRAM products! The only
databooks that list them are the old ones that I was about to have replaced!
Which means, while the companies ARE still producing 64K DRAMS for
"maintenance" purposes "ONLY," and those parts are available in the market,
I don't have any data on them!
256-K DRAM's (even 64K by 4) are ALMOST WITHOUT EXCEPTION 256 cycle refresh,
which means that they can NOT be used (with ease) with true Z80 (*&D#%ing,
eh!). MY SUGGESTION, at this point, would be to use 32K by 8 STATIC RAMS
(Hey, don't gasp...)!!! They are only $15 each, at most, these days int the
mail-order world, and are getting faster by the day. Pseudo-static RAMS
are not a bad idea, either.
For your information, Hyundai made 256-cycle DRAMS, and Motorola and Oki
made 128-cycle DRAMS. So did Mostek, but they merged with SGS-Thompson,
and no DRAMS in their databook! All 128-cyclers are 2mS refresh.
John Shin
P.S. Like I said, it would be also a good idea to get the brand of the
64K parts from the shop and ask the manufacturer, although telling a
256K chip that it is a 64K ship isn't such a bad idea, either.geertj@nlgvax.UUCP (Geert Jan de Groot) (07/26/89)
[In various articles, people proposed all kinds of solutions for the 128-cycle Z80 refresh problem. I still had my answer to the original writer lying around and thought it might be useful to others, so here it goes:] In article <398@uop.uop.EDU> he wrote: >I need 64Kx1 dynamic RAM chips, like 4164's. They need to be 100 ns. >They need to work with 7 bit (128 cycle) refresh. The most 64K DRAMs are 7 bit refresh. From memory, Hitachi, NEC, Fujitsu are all good. Texas Instruments is not. 128 or 256 bit refresh is clearly marked in the databook. 90% of the 64K RAMs (usually those from The Land Of The Rising Yen) are OK. If you still only get access to the remaining 10%, there is another trick using some extra circuitry. Get an extra 4040, connect the clock of the 4040 to RFSH of the Z80, and use Q7 as the extra refresh address you were missing. Use a 74153 as multiplexer for the extra addr pin: ---------- ---------- | | +---|I0 | | | | | | Z80 RFSH ---|clk Q7|-----------+---|I1 Q|--- new A7 4164's | | | | GND ---|reset | Z80 A14 ---|I2 | | | | | | | Z80 A15 ---|I3 | | | | | | | | | | HEF 4040 | ADDR MUX ---|A0 | ---------- | | Z80 RFSH ---|A1 | | | | 74LS153 | ---------- During R/W operation, A14/15 is fed to the RAM's, which you needed to build anyway because the old 4116's didn't have A7. During refresh, Q7 is fed to the RAMs. Because Q7 toggles each 128 refresh periods, it refreshes all columns. I hope this is clear enough. Good luck! >Am I the only one in the world who understands the difference between >7 and 8 bit refresh??? Am I going to have to buy 256K RAM chips and >waste 192K of RAM to make this project go??? 256K chips are even worse. They have 8/9 bit refresh, so you have 2 address bits to add. You can use Q8 of the 4040 and the other half of the 74153 to do this if you like, and have 256K available (with the multi-task, multi-user Z80 system I built with a group, we even have 384K available, enough to support 6 CP/M user simultaniously. How 384K is addressed with a Z80 is another story, available on request). >Nick Sayer | nsayer@uop.edu | ...ucbvax!ucdavis!uop!nsayer --8<--nip-nip--------------------------------------------------------------- Geert Jan de Groot, Email: geertj@nlgvax.pcg.philips.nl Philips TDS-ICA, ..!mcvax!nlgvax!geertj Innovation Centre Aachen, Ham: PE1HZG Weisshausstrasse, "MS-DOS is just a bootstrap" - me 5100 Aachen, Germany. phone: +49 241 6003 714 [Standard disclaimers apply]