Re: Results of Uthernet testing with Apple IIe and SN74LS245N

[a2retro@macgui.com (a2retro)]

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