Serial Interface Programming - Compaq Deskpro EP 6233 Technical Reference Manual

Chapter 5 Input/Output Interfaces
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
Serial Interface Configuration Registers
Index
Address Function
30h Activate
31h I/O Range Check
60h Base Address MSB
61h Base Address LSB
70h Interrupt Select
71h Interrupt Type
74h DMA Channel Select
75h Report DMA Assignment
F0h Configuration Data
5-16 Compaq Deskpro EP Series of Personal Computers
Table 5-10.
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
RO
R/W
First Edition – April 1998
Reset
Value
00h
00h
03h
F8h
04h
03h
04h
04h
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