开云体育

Sorry about an error in the flat pack chip I'm looking for. I wrote
TA7761P and should be TA7761F. Off topic.
Carl Hallberg (W9CJH)






On Wednesday, April 6, 2022, 12:02:35 PM CDT, Carl Hallberg via groups.io
<n9ess@...> wrote:





I have a whole tube of mcm68764L eproms. If these can replace the proms,
I will mail 5 to someone who can and wants to program them. I cannot find
data sheet on Google, so don't know specs. One of the eproms of the 5 I
did attempt to program and may or may not have been damaged. That is why 5
of them. I also have mcm68766, but may need them (or some) in the future
for Tek, HP? Will mail to contiguous United States. You pay postage. I am
looking for 2 Toshiba TA7761P. The description on internet is wrong, so
never attempted to purchase. Used in radio control.

By the way Raymond, the roms in the Commodore 64 were also Mostek. Maybe
why some of the failures.

Carl Hallberg (W9CJH)







On Wednesday, April 6, 2022, 10:33:35 AM CDT, Dave Wise <
david_wise@...> wrote:





The extra hardware for patching consisted of an FPLA (Field-Programmable
Logic Array) and a PROM. The FPLA monitored the address bus, and on
certain ranges it rerouted Chip Select from the mask roms to the patch
rom. From the processor’s point of view, this replaced a couple of
instructions with a jump that led to replacement code in the PROM, which
did its thing then jumped back to the mask ROM.

This scheme was used in 1980 in the 4024/4025/4027 terminals made by the
Information Display Division at the Wilsonville plant. Later models used
EPROMs, 2732 and up if I recall correctly.

Dave Wise
IDD 1980-1995

From: [email protected] <[email protected]> On Behalf Of Raymond Domp
Frank via groups.io
Sent: Tuesday, April 05, 2022 8:08 PM
To: [email protected]
Subject: Re: [TekScopes] (7854) A Drop-In Replacement for the MCM68766
EPROM

On Wed, Apr 6, 2022 at 04:41 AM, Carl Hallberg wrote:

The MCM68766 can always be replaced by a 2764 using a 28 dip socket to

24 dip

header. I don't have a 7854 and didn't look up the specs, but need to

check

the access time.

Physical space is the problem here, not electrical specs; the four 24-pin
ROMs are mounted end-to-end lengthwise with only 0.2" in between, which
doesn't allow for the longer 28-pin 2764's. on standard converting headers.
The two rows of two each that make up the total of four ROMs are 0.3"
apart. There would be enough space if one built a flat plug-in piggy-back
PCB and mounted the replacement EPROMs without sockets.

Standard MCM68766's (Ta <= 450ns) will do the job. I used them in one
7854. The bad IC's are not EPROMs (as Ram says) but mask ROMs, made by
Mostek. Some 'scopes are equipped with Motorola mask ROMs. Those don't
suffer from "ROM-rot". BTW, the board contains extra hardware that allows
patching of data in address ranges read from the ROMs, probably because it
was considered too slow and expensive to run new masks if a change was made.

Raymond