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 directly controlled by software through the I/O-mapped registers listed in Table 5-9.
Table 5–9
. Serial Interface Control Registers
Table 5-9.
Serial Interface Control Registers
COM1
Addr.
COM2
Addr.
Register
R/W
3F8h
2F8h
Receive Data Buffer
Transmit Data Buffer
Baud Rate Divisor Register 0 (when bit 7 of Line Control Reg. Is set)
R
W
W
3F9h
2F9h
Baud Rate Divisor Register 1 (when bit 7 of Line Control Reg. Is set)
Interrupt Enable Register
W
R/W
3FAh
2FAh
Interrupt ID Register
FIFO Control Register
R
W
3FBh
2FBh
Line Control Register
R/W
3FCh
2FCh
Modem Control Register
R/W
3FDh
2FDh
Line Status Register
R
3FEh 2FEh Modem
Status
R
5-10
Compaq D315 and hp d325 Personal Computers
Featuring the AMD Athlon XP Processor
Second Edition – April 2003
