TECH: 7474/74LS74
Peter van Os
Does anyone know if a 74LS74 will work instead of a 7474 on a Gottlieb
SYS80 MPU?
TIA,
Peter.
Clive Jones
<p.v...@uci.kun.nl> writes
>Hi,
>
>Does anyone know if a 74LS74 will work instead of a 7474 on a Gottlieb
>SYS80 MPU?
>
Peter, System 80's can be touchy with LS technology and cause
intermittent problems. I've seen some really spooky stuff HH did because
someone fit LS versions. As a rule, I'd stick with the non-LS TTL
(staright) version.
If you need some, drop me some mail and I'll get some out to you (no
charge).
Clive
Ray Johnson - Action Pinball
Any adverse problems using HC versions (74HC74)?
--
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Action Pinball & Amusement * Sales, Service, Parts, Repair *
Salt Lake City, Utah * Finest quality, best service- guaranteed *
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Clive Jones
<ra...@aros.net> writes
>Any adverse problems using HC versions (74HC74)?
>
Yes, the same rule applies.
HC series are pretty much drop-in replacements for LS or ALS except in a
few rare occassions (which I don't recall popping up in pins). The
caveat here is that HC<>LS should only be used when pull-up resistors
are already in-circuit. If you want to use HC as direct replacements for
LS with no pull-ups then you should use only HCT devices (the 'T'
indicates a built-in buffer stage for LS interfacing).
I can't find my standard TTL databook right now (typical, eh?) so I
can't see the input/output stage differences between straight TTL (for
example, the 7474 flip flop) and HCT. If it's just data, I can't see any
reason why HCT can't be used. If the gate sources or sinks current in
some form of driver circuit or has high fan-out, straight TTL still
seems to be the only option.
Clive
Ray Johnson - Action Pinball
Ray J.
--
Ed
But, this rule does not always apply. For example, (simply put) the clock oscillator circuit relies on the output
characteristics of a 7404 to create the oscillation. A 74LS04 or 74HCT04 should not be used in this position. A 74HC
part has less output drive, but has higher voltage rails - it is intended to work with CMOS devices such as 4000 series,
other 74HC series parts, many CMOS memories & processors, etc.. One needs to analyze the total load before subbing in a
74HC device. Also, there is a CMOS version of 7404 that can be used in a clock oscillator circuit -- 74HCU04. The U in
the middle stands for unbuffered. An unbuffered 74HCU04 will work quite well in an oscillator circuit -- but like the
other HC devices, you need to look at the load devices. In the case of a System 80 board, the load devices are 7474's
or 74LS74's. A 74HCU04 wouldn't be recommended in this position.
"Peter van Os" <p.v...@uci.kun.nl> wrote in message news:3B9C7B2B...@uci.kun.nl...
Steve Thomson
board exchange unit. I have found that Holley intake manifolds have the best
longevity of any I've tried. I you receive a "null cicuit" warning then you
may need to upgrade to a level 7 system override buffer. Hope that helps.
--
Steve Thomson (the second Steve)
StompS
Portland, OR
http://www.geocities.com/pdxinvestr/Stomps.html
Real Games:
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Pseudo Games:
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"Ed" <ekrz...@Home.com> wrote in message
news:_Adn7.6207$t9.22...@news1.rdc1.ne.home.com...
John Robertson
can drive 10 74XX gates or LOTS of LS gates.... so you can't reliably
sub LS for the regular 74XX devices...
John :-#)#
Ed
It's been many years since designing with low scale TTL -- working from memory (which ain't working well) I was thinking
that they both had the same IOH and IOL levels -- they don't. Straight TTL typically has a higher IOL level -- driving
more straight TTL gates. LS parts have much lower input level currents -- making them a lighter load. LS & HCT parts
can *usually* be subbed for straight TTL parts -- but only AFTER evaluating the load currents. Driving LS parts with
straight TTL usually works just fine. It's going the other way that can sometimes cause the problems. Also, the other
load devices must be accounted for (i.e. 6502 or ROMs).
-- Ed
"John Robertson" <j...@flippers.com> wrote in message news:9gbrpt07qhfm4kf6n...@4ax.com...
Ed
> can drive 10 74XX gates or LOTS of LS gates.... so you can't reliably
> sub LS for the regular 74XX devices...
>
> John :-#)#
>
nothing better to do. Most of the parts can be freely substituted. But many cannot. The clock oscillator circuit (Z3)
is one example of a part that cannot be subbed. Also, some IC's have hefty loads and cannot be subbed (some of the
7404's and a 7432). The 7474 in question on this board can be freely subbed with a 74LS74 or a 74HCT74. I went through
all the standard logic devices on the Gottlieb System 80 MPU. Based on loading and ouput characteristics, this is what
I get as valid subs for the System 80 MPU:
Z1 = 4528
Do not substitute
Z2 = 7474
Acceptable subs are 74LS74 and 74HCT74
Z3 = 7404
Do not substitute
Z4 = 4081
Do not substitute
Z7 = 74LS04
Acceptable sub is 74HCT04
Z8 = 7402
Acceptable subs are 74LS02 and 74HCT02
Z9 = 7400
Acceptable subs are 74LS00 and 74HCT00
Z10 = 74LS05
Do not substitute
Z11 = 7404
Do not substitute
Z12 = 7404
Do not substitute
Z13 = 7400
Acceptable subs are 74LS00 and 74HCT00
Z14 = 7400
Acceptable subs are 74LS00 and 74HCT00
Z15 = 7432
Do not substitute
Z16 = 7404
If Z18, 20, and 22 are 74175, do not substitute
If Z18, 20, and 22 are 74LS175 or 74HCT175, acceptable subs are 74LS04 and 74HCT04
Z17 = 7404
Acceptable subs are 74LS04 and 74HCT04
Z18 = 74175
Acceptable subs are 74LS175 and 74HCT175
Z19 = 7448
Acceptable sub is 74LS48
Z20 = 74175
Acceptable subs are 74LS175 and 74HCT175
Z21 = 7448
Acceptable sub is 74LS48
Z22 = 74175
Acceptable subs are 74LS175 and 74HCT175
Z23 = 7448
Acceptable sub is 74LS48
Z24 = 7404
Acceptable subs are 74LS04 and 74HCT04
Z25 = 74154
Acceptable subs are 74LS154 and 74HCT154
Z26 = 7404
Acceptable subs are 74LS04 and 74HCT04
Z27 = 7404
Acceptable subs are 74LS04 and 74HCT04
Z28 = 74LS139
Acceptable sub is 74HCT139
Z29 = 7416
Acceptable sub is 7406
Z30 = 7416
Acceptable sub is 7406
Z31 = 7408
Acceptable subs are 74LS08 and 74HCT08
Z32 = 7417
Acceptable sub is 7407
Z33 = 74154
Acceptable subs are 74LS154 and 74HCT154
Z34 = 7404
Acceptable subs are 74LS04 and 74HCT04
Z35 = 7404
Acceptable subs are 74LS04 and 74HCT04
Z36 = 4069
Do not substitute
Of course, substituting some of the parts will ripple through and allow others to be substituted as well - but this can
get quite convoluted.
Some of the devices used by Gottlieb for off-board connections should have never been used -- i.e. - logic shouldn't go
off board, only dedicated drivers & receivers should go off board... but this is a mute point.
Just my opinions --
-- Ed
John Robertson
are widely available... Nice piece of work, mind you...if you are
looking for a job drop by sometime.
John :-#)#