Compaq EN Series Technical Reference Manual page 94

Configuration Byte C7h, C8h, Serial Ports 1 and 2 (Respectively) Configuration Bytes
Default Value = FEh, 7Dh
Bit Function
7..2 Base I/O Address (in packed format)
(Algorithm: [Addr. - 200h] / 8)
(i.e., 3Fh = 3F8h, 1Fh = 2F8h, 00 = 200h)
1..0 Interrupt:
00 = Reserved
01 = IRQ3
10 = IRQ4
11 = Reserved
Configuration Bytes CAh, DBh; Chassis Serial Number
Configuration Bytes DEh, DFh; Checksum of Locations 90h-DDh
Configuration Bytes E0h-FFh; Client Management Error Log
Compaq Deskpro EN Series of Personal Computers
Desktop and Minitower Form Factors
Third Edition - September 1998
Technical Reference Guide
4-45