Compaq Deskpro EP 6233 - Serial Interface Programming

Chapter 5 Input/Output Interfaces
5-16 Compaq Deskpro EP Series of Personal Computers
First Edition – April 1998
5.4.2 SERIAL INTERFACE PROGRAMMING
5.4.2.1 Serial Interface Configuration
The serial interfaces must be configured for a specific address range (COM1, COM2, etc.) and
also must be activated before it can be used. Address selection and activation of the serial
interface are affected through the PnP configuration registers of the 87309 I/O controller.
The PnP configuration registers are accessed through I/O registers 15Ch (index) and 15Dh
(data). The serial interfaces are initiated by firmware selecting logical device 2 and 3 of the
87309. This is accomplished by the following sequence:
1. Write 07h to I/O register 15Ch.
2. Write 02h (for UART2) or 03h (for UART 1) to I/O register 15Dh.
3. Write 30h to I/O register 15Ch.
4. Write 01h to I/O register 15Dh (this activates the interface).
The serial interface configuration registers are listed in the following table:
Table 5–10
. Serial Interface Configuration Registers
Table 5-10.
Serial Interface Configuration Registers
Index
Address Function R/W
Reset
Value
30h Activate R/W 00h
31h I/O Range Check R/W 00h
60h Base Address MSB R/W 03h
61h Base Address LSB R/W F8h
70h Interrupt Select R/W 04h
71h Interrupt Type R/W 03h
74h DMA Channel Select R/W 04h
75h Report DMA Assignment RO 04h
F0h Configuration Data R/W --