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Re: Results of Uthernet testing with Apple IIe and SN74LS245N

mwillegal wrote:

Hi,

PC suffix means plastic DIP package to Fairchild and Moto and perhaps others
N suffix means plastic DIP package to TI and many others.

So difference is more likely variation between manufacturers, which should not be very significant for LS series parts.  Note that differences between the data sheets can be due to variations in manufacturers qualification process.  The package type has little bearing on chip performance.  Another option to solve the problem may be to look at substituting a different technology pin compatible part, which has more margin for this application.

Regards,
Mike Willegal


I agree, Mike--any timing differences between manufacturer's LS chips
should be inconsequential.

The fact that it makes a difference, and that adding a super serial
card load disturbs the bus timing enough to cause failures suggests
that the Uthernet card has very little timing margin in a //e machine.

A proper analysis would call for using a scope to check whether the
setup and hold times are being met by the card.

This is a problem with limited-run cards.  The card may work fine
in most machines but not all, as a result of small timing margin
differences.  A proper card design has sufficient timing margin
to work not only with all specified bus tolerances, but even somewhat
outside those tolerances, to provide good reliability.


On Saturday, April 14, 2012 7:26:28 PM UTC-4, D Finnigan wrote:


Some people may remember back in November I was testing the Uthernet on my
unenhanced IIe and II Plus to see if I could get it to work reliably with
Contiki and ADTPro. I found that I had to remove almost every other card in
order for it to work.

About a week ago, Glenn Jones told me that another Uthernet user was having
a similar problem. He noticed that some cards had a 74LS245PC instead of a
74LS245N. It turns out that replacing the PC with the N solves the problem.
Complete notes in my blog: 
Part 1- http://www.macgui.com/blogs/?e=383

Part 2- http://www.macgui.com/blogs/?e=384

--
]DF$
Mac GUI Vault - A source for retro Apple II and
Macintosh computing.
http://macgui.com/vault/


--

-michael

NadaNet 3.1 for Apple II parallel computing!
Home page:  http://home.comcast.net/~mjmahon/

"The wastebasket is our most important design
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