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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.