26 Mar
2008
26 Mar
'08
6:20 a.m.
Hello All
As I said before my PDP-8/e partly failed insofar as it would
not load data into memory.
I rewound my personal memory back thirty plus years and did a lot of
relearning about how pre microprocessor systems worked.
Toggling the Add Load switch puts the address on the bus and triggers
the time state generator to cycle.
In the correct time slot the address is set in the memory ready for the
data.
Setting the Switch Register with the data and toggling the DEP key
should write data from the SR to the pre set memory location via the bus
in another time slot.
The time states are generated by a string of SN74194 shift registers and
the slot for the data is not being decoded. It looks like the '194 is at
fault.
Now I need either a couple of 74194's or an M8330 board.
Rod Smallwood
TheDECcollector
27 Mar
27 Mar
7 a.m.
Date: Wed, 26 Mar 2008 13:20:59 +0000
From: RodSmallwood at mail.ediconsulting.co.uk
To: cctech at classiccmp.org
CC:
Subject: Looking for a M8330 or a couple of SN74194's
Hello All
As I said before my PDP-8/e partly failed insofar as it would
not load data into memory.
I rewound my personal memory back thirty plus years and did a lot of
relearning about how pre microprocessor systems worked.
Toggling the Add Load switch puts the address on the bus and triggers
the time state generator to cycle.
In the correct time slot the address is set in the memory ready for the
data.
Setting the Switch Register with the data and toggling the DEP key
should write data from the SR to the pre set memory location via the bus
in another time slot.
The time states are generated by a string of SN74194 shift registers and
the slot for the data is not being decoded. It looks like the '194 is at
fault.
Now I need either a couple of 74194's or an M8330 board.
Rod Smallwood
TheDECcollector
Hi
A quick search on the web shows that both Anchor Electronics and
Jameco carry 74194's. I'd expect others carry them as well.
Dwight
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9:03 a.m.
Rod Smallwood wrote:
Hello All
As I said before my PDP-8/e partly failed insofar as it would
not load data into memory.
I rewound my personal memory back thirty plus years and did a lot of
relearning about how pre microprocessor systems worked.
Toggling the Add Load switch puts the address on the bus and triggers
the time state generator to cycle.
In the correct time slot the address is set in the memory ready for the
data.
Setting the Switch Register with the data and toggling the DEP key
should write data from the SR to the pre set memory location via the bus
in another time slot.
The time states are generated by a string of SN74194 shift registers and
the slot for the data is not being decoded. It looks like the '194 is at
fault.
Now I need either a couple of 74194's or an M8330 board.
TTL can be found here:
http://www.unicornelectronics.com/prod.htm
Rod Smallwood
TheDECcollector
3:25 p.m.
Now I need either a couple of 74194's or an M8330
board.=20
The former being a lot easier to find than the latter, quite apart from
the moral aspect of keeping the machine as original as possible.
I don;t know if they have them, but have you tried Cricklewood
Electronics? They had some 74(LS)95 chips when I needed them to repair an
old HP machine, and seem to be the only place that did.
-tony
28 Mar
28 Mar
8:01 p.m.
Now I need
either a couple of 74194's or an M8330 board.
I don;t know if they have them,
but have you tried Cricklewood
Electronics? They had some 74(LS)95 chips when I needed them to
repair an old HP machine, and seem to be the only place that did.
8:22 p.m.
der Mouse wrote:
Of course, depending on how non-original you're
willing to be....
A 74F194 would be a better replacement I suspect over a 74194.
Now does a persion here have a list of common replacement parts
and rare parts. This 2008 and I don't expect spares to around much longer.
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.
9:12 p.m.
Date: Fri, 28 Mar 2008 21:22:10 -0600
From: bfranchuk at jetnet.ab.ca
To:
Subject: Re: Looking for a M8330 or a couple of SN74194's
der Mouse wrote:
Hi
Anchor list 74194, 74LS194, 74S194, 74HC194 and 74F194. They also
have 7495s.
SO, what is the problem?
Dwight
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Of course, depending on how non-original
you're willing to be....
A 74F194 would be a better replacement I suspect over a 74194.
Now does a persion here have a list of common replacement parts
and rare parts. This 2008 and I don't expect spares to around much longer.
29 Mar
29 Mar
7:37 a.m.
Date: Fri, 28 Mar 2008 23:06:15 -0600
From: bfranchuk at jetnet.ab.ca
To:
Subject: Re: Looking for a M8330 or a couple of SN74194's
dwight elvey wrote:
Hi
The time may come that these part become hard to get but
unless someone burns down places like Anchor and Unicorn,
they'll be there for some time.
My point is that most of these are still available. The fellow that needs
one can still buy the correct replacement.
Since both companies sell NOS parts, one might even get a good
date code.
I expect that someday, the supply will run dry. There are a few
parts that are already getting hard to find. 74S38 are one of them.
The ones that are really bad are the custom parts. The ROM chip
for the KIM is a good example.
I have a board that is waiting for a bus inteface chip. I watch
but don't have a lot of hope.
Dwight
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Hi
Anchor list 74194, 74LS194, 74S194, 74HC194 and 74F194. They also
have 7495s.
SO, what is the problem?
Dwight
So for how long. At least unicorn has a '*' beside the TTL
that is no longer manufactured. That is a good chunk of them.
1:56 p.m.
woodelf wrote:
A 74F194 would be a better replacement I suspect over
a 74194.
If a machine was designed for a 74194, a 74F194 will at best be an
adequate replacement, but it won't be better.
The 74F194 is faster, but that isn't necessarily an improvement.
As part of being faster, it has faster edge (slew) rates on its
outputs, which can cause problems. It also draws higher transient
currents.
Eric
2:39 p.m.
der Mouse wrote:
[Using other logic families]
> Of course, depending on how non-original you're willing to be....
There are problems, of course, when either the original chip never
existed in a different logic family, or when it has significantly
different pinouts or even characteristics. Certainly some 74Lxx numbers
are different to the 74LSxx part of the same number, and I think there's
one chip in the 7470-ish area) that has rather different functions in 2
logic families (I can look it up if you like).
This doesn't apply to the '194 AFAIK. It has made life 'interesting' for
me, though. I prefer, of course, to keep the original family, but I'd
rather fit a substitute than have a non-working machine. Computers are
not there to look nice on the shelf :-)
-tony
5886
days inactive
5889
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11 comments
6 participants
participants (6)
-
ard＠p850ug1.demon.co.uk -
bfranchuk＠jetnet.ab.ca -
dkelvey＠hotmail.com -
eric＠brouhaha.com -
mouse＠Rodents.Montreal.QC.CA -
RodSmallwood＠mail.ediconsulting.co.uk