Re: 6569 luminances

From: Jim Brain <>
Date: Mon, 14 May 2012 13:09:37 -0500
Message-ID: <>
On 5/14/2012 12:34 PM, Gerrit Heitsch wrote:
> With a CMOS-EPROM it's not much, but there are still a few NMOS-EPROMs 
> around that could get used and with them it makes a difference, at 
> least in heat output.
I would never recommend power hungry NMOS EPROM in a replacement.
>>   * I was worried that the delay of enabling the ROM and it's output
>>     drivers would cause timing issues. On a 250nS 27C64, it can take up
>>     to 350nS from !CE to data valid. That's compared to 120nS for !OE to
>>     data valid.
> Where did you get the 350ns for a  250ns EPROM? I'm looking at the 
> datasheet for a 27C64 from NS and that one states that for a 250ns 
> type,  tCE (_CE to output delay) is 250ns and 350ns for a 27C64-350. 
> In that datasheet the times are supplied in a table and can be 
> misread. Since you mentioned 120ns (which is tOE for the 27C64-350, 
> the 27C64-250 has a tOE of 70ns), you might want to take another look 
> at that datasheet you used.
Sorry, I mean 350nS 27C64 above.  You  are correct that 250nS has 250 
and 70.
>> If folks are sure the two can be tied together, please let me know.
> I have done it and didn't get any complaints from the circuits I used 
> that in yet, namely 1541 and C64.
Well, that's nice, but hardly an exhaustive set of tests.
>  Gerrit

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Received on 2012-05-14 19:00:22

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