Re: 6569 luminances

From: MikeS <>
Date: Mon, 14 May 2012 16:44:04 -0400
Message-ID: <BCEA997D91564D24A74D00B55624E285@vl420mt>
----- Original Message ----- 
From: "Gerrit Heitsch" <>
Sent: Monday, May 14, 2012 3:11 PM

> On 05/14/2012 08:45 PM, MikeS wrote:

>> Eh? Say what? AFAIK, with /CE low the time it takes to get valid data is
>> tOE, e.g. 50ns vs. 200ns in a -200 'C256 (not that it matters at 1MHz).
> No, there is also tACC, the time from address input valid to data output
> valid. And that is the time printed on the EPROM and, in most cases, the
> same time as tCE. You can hide tOE inside tACC, but you cannot go below
> tACC. tOE is the time to get the output drivers up, but if tACC is not
> over by then, you get lots of things but not valid data.
>  Gerrit
Yes, but the address will have been valid for some time by the time /CS goes
low after the delays in the CPU and PAL.

IMHO the issue (if any of this is indeed an issue) is that a 250ns 2364 has
an address access time of 250ns but a CS access time of *only 100ns*,
whereas a 250ns 27Cxxx also has a 250ns address access time but a CE access
time equal to tACC, i.e. *250ns*, so it seems to me that keeping /CE low and
using /OE with its 50ns delay would be preferable and on the safe side.


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Received on 2012-05-14 21:00:21

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