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**sorry for slighltly off topic, i dont have anyone else to ask immediately** Question: Will there be a problem with me substituting '74LS' parts for a circuit that uses '74HCT' The parts in question are: 74hct259 and 74hct574 The circuit in question is at: http://www.ibiblio.org/pub/Linux/apps/circuits/EEP-0.2.html (it is a circuit for burning eeproms using parallel port on a computer) thanks for help, bob d

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On Mon, Jun 03, 2002 at 03:15:49PM -0500, Technical Operations wrote: > **sorry for slighltly off topic, i dont have anyone else to ask immediately** > > Question: > Will there be a problem with me substituting '74LS' parts for a circuit that > uses '74HCT' > > The parts in question are: 74hct259 and 74hct574 > > The circuit in question is at: > http://www.ibiblio.org/pub/Linux/apps/circuits/EEP-0.2.html > > (it is a circuit for burning eeproms using parallel port on a computer) Probably not going to be a problem. Then again I presume you have LS parts but do not have HCT parts, hence your question. Socket the board you build. If LS doesn't work then it will be easy to put HCT in the sockets and see if that cures the problem. 74HCT family will drive output levels in excess of 3.0 volts, usually to within a hair's width of your supply rail. A plain old 74LS is not guaranteed to output more than 2.7v on 5.0v supply. When programming an EPROM one is really operating the device in a linear mode where all the input voltages are important. Or may be important. To properly verify your EPROM is well programmed it should be read at 5.5v and 4.5v supply levels. Good commercial programmers do. -- David Kelly N4HHE, ===================================================================== The human mind ordinarily operates at only ten percent of its capacity -- the rest is overhead for the operating system.

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Hi bob d, > Will there be a problem with me substituting '74LS' parts for > a circuit that > uses '74HCT' There might well be. I believe the minimum High input voltage to the HC16 is 0.7*Vcc = 3.5 v. Anything below this may not be registered as a high. I do not believe that the 74LS parts can guarantee a High output in ecess of 3.5v. Good luck, Bob Furber __________________________________________________________ Connect your micro to the internet the easy way www.microcommander.com Microcontroller with an obscenity of I/O & features ..in a small footprint www.steroidmicros.com __________________________________________________________

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> I do not believe that the > 74LS parts can guarantee a High output in ecess of 3.5v. You can get a wider swing by adding a pull-up resister, but in the case of a $1 part you should just get the right thing.

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At 2002-06-03 15:15 -0500, Technical Operations wrote: >Question: >Will there be a problem with me substituting '74LS' >parts for a circuit that uses '74HCT' > >The parts in question are: 74hct259 and 74hct574 > >The circuit in question is at: >http://www.ibiblio.org/pub/Linux/apps/circuits/EEP-0.2.html > >(it is a circuit for burning eeproms using parallel port on a computer) Besides, what the other guys said, please consider that CMOS inputs may not be left open. HCT means High-speed CMOS TTL-compatible. This in case you're substituting LS by HCT and not the other way round. You can read more about different TTL-families: http://www.chipdir.org/ttl.htm By the way, I agree with Clifford Heath that it's better to get the right parts at the low prices for these parts. Especially when the design calls for HCT (which is the 'future'). HCT also uses less energy, so when you're planning to use LS instead of HCT you may also be using too much energy in the design in question. Greetings, Jaap -- Chip Directory -- http://www.chipdir.org/ -- http://www.chipdir.nl/ -- And about 35 other mirror sites world-wide. -- -- To subscribe to a free 'chip issues, questions and answers' -- mailing list send a message to with -- in the body 'subscribe chipdir-L'.

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> By the way, I agree with Clifford Heath that it's > better to get the right parts at the low prices > for these parts. Yes, i agree. Thank you for the link. I just wanted to use LS parts because thats all i can get immediatly. In st. louis we have 2 electronics outlets and neither of them had the right parts. guess it will be digi-key for me. thanks for everyones help bd

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