Compaq 850 manual Serial Interface Control Registers, Addr Register

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	COM2
Addr.	Addr.	Register	R/W
3F8h	2F8h	Receive Data Buffer	R
		Transmit Data Buffer	W
		Baud Rate Divisor Register 0 (when bit 7 of Line Control Reg. Is set)	W
3F9h	2F9h	Baud Rate Divisor Register 1 (when bit 7 of Line Control Reg. Is set)	W
		Interrupt Enable Register	R/W
3FAh	2FAh	Interrupt ID Register	R
		FIFO Control Register	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

5-10Compaq Deskpro EXS and Workstation 300 Personal Computers

Featuring the Intel Pentium 4 Processor

First Edition – December 2000