IBM B50 - Manual (Page 187)

PCI Base
Class
(lower
nibble) S2
PCI
Sub-Class
S3 -S4
Description
6
Bridge devices
00 Host bridge
01 ISA bridge
02 EISA bridge
03 MCA bridge
04 PCI-to-PCI bridge
05 PCMCIA bridge
06 NuBus bridge
07 Cardbus bridge
80 Other bridge device
7
Simple communication controllers
00 Serial controllers
01 Parallel port
80 Other communication controllers
8
Generic system peripherals
00 PIC
01 DMA controller
02 System timer
03 Real-Time Clock (RTC) controller
80 Other system peripherals
9
Input devices
00 Keyboard controller
01 Digitizer (pen)
02 Mouse controller
80 Other input controllers
A
Docking stations
00 Generic docking station
80 Other type of docking station
Appendix A. Interpreting Firmware Error Codes A-3