I have managed to figure out that the bottom row of pins in the EISA riser card slot are for the 2 PCI bus card + 3 ISA breakout board. I have reverse engineered the pin-out in hopes that someone can make a PCB for this motherboard giving it PCI slots. Sorry about the poor formatting.
Gnd A 1 B Gnd
Gnd A 2 B Gnd
INTC# A 3 B INTA#
INTD# A 4 B INTB#
+5V A 5 B +5V
+5V A 6 B +5V
CLK A 7 B RST# -
Gnd A 8 B Grant0
Grant1 A 9 B Request0
Gnd A 10 B Gnd
Request1 A 11 B CLK
- AD 31 A 12 B Gnd
- AD 29 A 13 B AD 30 -
N/C? A 14 B N/C?
N/C? A 15 B N/C?
- AD 27 A 16 B AD 28 -
- AD 25 A 17 B AD 26 -
* C/BE3# A 18 B AD 24 -
- AD 23 A 19 B AD 22 -
- AD 21 A 20 B AD 20 -
- AD 19 A 21 B AD 18 -
N/C? A 22 B N/C?
- AD 20 A 23 B AD 19 (Used for IDSEL (Init Device Select for each PCI slot)) -
- AD 17 A 24 B AD 16 -
- IRDY# A 25 B Frame# *
- DEVSEL# A 26 B C/BE2# *
Lock A 27 B Target Ready *
** PERR# A 28 B STOP# -
SERR# A 29 B N/C (Snoop done on a Pentium class riser)
- AD 15 A 30 B N/C (Snoop backoff on a Pentium class riser)
- AD 14 A 31 B C/BE1# *
- AD 12 A 32 B PAR -
Gnd A 33 B Gnd
Gnd A 34 B Gnd
- AD 10 A 35 B AD 13 -
- AD 8 A 36 B AD 11 -
- AD 7 A 37 B AD 9 -
- AD 5 A 38 B C/BE0# *
- AD 3 A 39 B AD 6 -
- AD 1 A 40 B AD 4 -
- AD 0 A 41 B AD 2 -
+5V A 42 B +5V
+5V A 43 B +5V
Gnd A 44 B Gnd
Gnd A 45 B Gnd
All the pins with a - in front or behind are directly connected to other PCI devices, no buffer or other chips. IDSEL is connected to AD22 for the graphics chip and AD21 for the PCI IDE controller chip. The pins with a * in front or behind have a 33 ohm resistor connected between that pin and the bus and the pin with a ** has a 82 ohm resistor connected to the PCI IDE chip and I am not sure where else it goes (it has a 4.7K ohm pullup to the +5V rail as well). Any of the pins with a ? by them are not connected on this motherboard but on a Pentium class system they are for the 3.3V rail for the PCI slot.