IRQ problems with SSC (???)

[mkelsey@rayshade.eecs.wsu.edu (Michael Kelsey - EECS (Cpts499))]

Hello all,

	I have a PC (80x86) that permits the user to assign IRQ's to certain
peripherals.  Of course, the lower the number of the IRQ, the higher the
priority.    
	Not too long ago I finally got a ThunderClock for my Apple II, but
for the life of me, I couldn't get a smooth transfer between my Apple II
and my PC's COMx port!  I found this *very* frustrating since I couldn't
discern the problem.  Finally, I removed the ThunderClock from slot 5 and
discovered that all of my communications problems disappeared!  Amazing but
true.  I then scanned in my //e Technical Reference and found out that slot 7
has a higher IRQ priority than slot 6...and so forth.  So, I migrated my SSC
(initially in slot 1 - for printer reasons) to slot 2 and placed the Thunder-
clock to slot 1.  When I tried out my theory, all communications problems
ended.    
	Does anyone know if this is due to ProDOS getting called by the inter-
rupt and denying the terminal program its service to the SSC?  And just re-  
cently, I snagged a Digital Research Z-80 CP/M interface card (which I believe
goes in slot 4 - so much for the mouse) and it caused the same type of pro-
blem that I experienced earlier.  Sure enough, after removing it from slot
4 (and leaving it out) my SSC conflicts stopped and the data transfered at
19200 baud flawlessly.  So, does the Z-80 have this same type of interrupt?
I lack any information about the Z-80 (drivers and docs) and therefore have
no manner by which to test the interface...should a Z-80 cause this type
of interference?

	Thanks in advance!

-Michael-