Parallel Interface Programming - Compaq Deskpro EP 6233 Technical Reference Manual

5.5.4

PARALLEL INTERFACE PROGRAMMING

5.5.4.1 Parallel Interface Configuration
The parallel interface must be configured for a specific address range (LPT1, LPT2, etc.) and
also must be enabled before it can be used. When configured for EPP or ECP mode, additional
considerations must be taken into account. Address selection, enabling, and EPP/ECP mode
parameters of the parallel interface are affected through the PnP configuration registers of the
87309 I/O controller. Address selection and enabling are automatically done by the BIOS during
POST but can also be accomplished with the Setup utility and other software.
The PnP configuration registers are accessed through I/O registers 15Ch (index) and 15Dh
(data). The parallel interface is initiated by firmware selecting logical device 4 of the 87309. This
is accomplished by the following sequence:
1. Write 07h to I/O register 15Ch.
2. Write 01h to I/O register 15Dh (for selecting the parallel interface).
3. Write 30h to I/O register 15Ch.
4. Write 01h to I/O register 15Dh (this activates the interface).
The parallel interface configuration registers are listed in the following table:
Table 5–12. Parallel Interface Configuration Registers
Parallel 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
Table 5-12.
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
RO
R/W
Compaq Deskpro EP Series of Personal Computers
First Edition - April 1998
Technical Reference Guide
Reset
Value
01h
00h
02h
78h
07h
00h
04h
04h
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