[time-nuts] HP8568B firware eproms anyone ?

Robert Atkinson robert.atkinson at genetix.com
Fri Oct 20 04:01:30 EDT 2006


Hi John,
After much experience swapping ROM's and EPROM's in commercial
equipment, I've found that you can never be sure of using a new part.
The address and control timing on many designs is not all it should be,
often the system is only working due to marginal (or even totally
incorrect) timing. Changes in propagation delays can wreak havoc. In
particular I've seen problems were the supposedly identical new device
(same part number, same manufacturer) has been migrated to a smaller
die. This reduces propagation delays (the specs give a maximum delay not
a minimum!) causing system failure. At least with UV-EPROM's you can see
the difference in die size, sometimes it's huge. 
I guess that not many equipment manufacturers measure their timing and
ensure adequate margins, unless it doesn't work first time. Shrinking
die size's can also be an issue with analogue devices with reduced
output drive capacity and poorer stability / noise rejection being most
common.

Robert G8RPI.

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of John Miles
Sent: 19 October 2006 17:54
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] HP8568B firware eproms anyone ?

Heh, that's great.  Interesting that at least some CMOS parts will work.
I
may have had some bad chips, but the same ones that failed in an 8566B
worked fine in a 494AP.

Not knowing what happens if an address line toggles in the middle of a
read
cycle, I wonder if it'd be a good idea to tie those floating address
lines
to ground or Vcc...

-- john, KE5FX

>
> In message <PKEGJHPHLLBACEOICCBJOEKDIJAA.jmiles at pop.net>, "John
> Miles" writes:
>
> >Poul, if you need a set of them burned for you, drop me a line
> >off-list with your address... be glad to send you some.
>
> Thanks for the offer, but I managed to wing it.
>
> >Note that the part number may cross to a 27C256, but I have had no
luck
> >trying to use CMOS EPROMs in the HP 8566B/68B analyzers.
>
> Well here is a different data-point for you: ...
>
>


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