Re: Results of Uthernet testing with Apple IIe and SN74LS245N

[Michael J. Mahon <mjmahon@aol.com>]

a2retro <a2retro@macgui.com> wrote:
> Hi Guys
> 
> Michael J. Mahon wrote:
>> 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.
> 
> "should be" isn't correct in this case. I assumed that as well as my Apple
> IIe 80 column card uses a 74LS245PC but upon some investigation I found out
> that there are noted differences in the timing between these two parts.
> Enough to make a difference as far as gluing a CS8900A to the bus is
> concerned anyway. 
> 
> Prop delay  - TI = 8 (max 12)             .... Fairchild = 18
> OE Enable  - TI = 25/27 (max 40/40)  .... Fairchild = 25/30
> OE disable - TI = 15/15 (max 25/28)  .... Fairchild = 25/18
> 
> So it would appear the 74LS245PC is to slow in this design as I have had
> consistent results using a "N" part in a IIe.
> 
> Cheers
> 
> Glenn

Um, that's Mike Willegal, not me. ;-)

-michael - NadaNet 3.1 and AppleCrate II: http://home.comcast.net/~mjmahon