XT slots (was: RE: IBM 5161 - test-drb@ccmp.vtda.org

2 Apr 2003

after checking in my IBM XT reference manual, the fact is that
they added a buffer to the normal data and address bus and sent
buffered these signals into J8. Also, they added a 14.318mhz
oscillator on the expansion chassis side because they did not
want pass this high of a frequency over the cable. This does
mean that the manin 14mhz and the expansion chassis 14mhz are
not in phase.
The added buffers make the timning in slot 8 a littl emore tight
because of the added delays through the additional chips. Slot
8 also had a requirement that it supply a card selected signal
back to make sure the card was really ready to be accessed.

The buffering from an engineering standpoint was done to increase
the drive on the cable to the expansion chassis as well as help
isolate the rest of the system bus from any added capacitance
and noise from the outside world.

best regards, Steve Thatcher
...
 --- Original Message ---
From: "Fred Cisin (XenoSoft)" &lt;cisin(a)xenosoft.com&gt;
To: cctalk(a)classiccmp.org
Date: 4/2/03 12:36:58 PM

  >But in the XT, one slot is different.
 > Why? 
On Wed, 2 Apr 2003, Ethan Dicks wrote:
> decided it was easier to give away a serial card than deal with the
...
 > customer-support issue of random 3rd-party cards
not working in that
...
   slot. 
But "WHY?"
Did they leave off the buffer chip BECAUSE the serial card didn't need it?
...
 Or did they use the serial card to cover up a MISTAKE?
Or did they have some OTHER plan for it, and used the serial card as a
...
 "placeholder"? 