Table 5-11. Serial Interface - Compaq EN Series Technical Reference Manual

Chapter 5 Input/Output Interfaces
5.4.2.2 Serial Interface Control
The BIOS function INT 14 provides basic control of the serial interface. The serial interface can
be controlled by software through the registers listed in Table 5-11.
Table 5–11. Serial Interface Control Registers
Address
Base
Base, Base + 1
Base + 1
Base + 2
Base + 3
Base + 4
Base + 5
Base + 6
Base + 7
NOTES:
Base Address:
[1] This register holds receive data when read from and transmit data when written to.
[2] When bit <7> of the Line Control register is set (1), writing to 3F8h and 3F9h
programs the divisor rate for the baud rate generator.
Receive Buffer / Transmit Holding Register, I/O Port 3F8h/2F8h
When read by the CPU, this byte contains receive data. When written to by the CPU, the byte
contains data to be transmitted.
5-16 Compaq Deskpro EN Series of Personal Computers
Net PC and Small Form Factor Models
Table 5-11.
Serial Interface Control Registers
Register
Receive Buffer / Transmit Holding [1]
Baud Rate Divisor Latch [2]
Interrupt Enable
Interrupt ID
Line Control
Modem Control
Line Status
Modem Status
Scratch Pad
COM1 = 3F8h
COM2 = 2F8h
First Edition – June 1998
R/W
R/W
R/W
R/W
RO
R/W
R/W
RO
RO
R/W