Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 (Tek) 9/28/84 based on 9/17/84; site azure.UUCP Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!mhuxt!houxm!vax135!cornell!uw-beaver!tektronix!teklds!azure!michaelk From: michaelk@azure.UUCP (Mike Kersenbrock) Newsgroups: net.micro Subject: Re: Z-80 and DRAMs Message-ID: <429@azure.UUCP> Date: Fri, 23-Aug-85 01:10:54 EDT Article-I.D.: azure.429 Posted: Fri Aug 23 01:10:54 1985 Date-Received: Sun, 25-Aug-85 05:34:22 EDT References: <2268@sdcrdcf.UUCP> Organization: Tektronix, Beaverton OR Lines: 16 > I am tossing together a micro with a Z-80 and lots of memory (at least 64K). > The natural choice is DRAMs. There will be eight sockets and the design should > be able to accept 64K or 256K parts. > > The problem is refresh. > > To keep parts low, the Z-80's built-in refresh timing will be used. Sadly, the > Z-80's internal refresh counter is only 7 bits wide. This will take care of > some of the 64K chips on the market, but not all of them. All of the 256K DRAM > specs that I have seen require 8 bits of refresh (luckily not 9). 1.- Use one of the CMOS Z80s, like the NSC800 which if memory serves me right, has the 8th bit. 2.- Add JUST the 8th bit. If parts count is a problem, you could "do it" with a single PAL package.