Table 5-10. Parallel Interface; Table 5-11. Parallel Interface - Compaq Deskpro Workstation AP230 Technical Reference Manual

Chapter 5 Input/Output Interfaces
5.5.4.2 Parallel Interface Control
The BIOS function INT 17 provides simplified control of the parallel interface. Basic functions
such as initialization, character printing, and printer status are provide by subfunctions of INT 17.
The parallel interface is controllable by software through a set of I/O mapped registers. The
number and type of registers available depends on the mode used (SPP, EPP, or ECP). Table 5-11
lists the parallel registers and associated functions based on mode.
Table 5–11. Parallel Interface Control Registers
I/O
Address
Base
Base + 1h
Base + 2h
Base + 3h
Base + 4h
Base + 5h
Base + 6h
Base + 7h
Base + 400h
Base + 400h
Base + 400h
Base + 400h
Base + 401h
Base + 402h
Base Address:
LPT1 = 378h
LPT2 = 278h
LPT3 = 3BCh
5-14 Compaq Deskpro Personal Computers
Table 5-11.
Parallel Interface Control Registers
Register
Data
Printer Status
Control
Address
Data Port 0
Data Port 1
Data Port 2
Data Port 3
Parallel Data FIFO
ECP Data FIFO
Test FIFO
Configuration Register A
Configuration Register B
Extended Control Register
Third Edition – April 2001
SPP EPP
Mode Mode
Ports Ports
LPT1,2,3 LPT1,2
LPT1,2,3 LPT1,2
LPT1,2,3 LPT1,2
-- LPT1,2
-- LPT1,2
-- LPT1,2
-- LPT1,2
-- LPT1,2
-- --
-- --
-- --
-- --
-- --
-- --
ECP
Mode
Ports
LPT1,2,3
LPT1,2,3
LPT1,2,3
--
--
--
--
--
LPT1,2,3
LPT1,2,3
LPT1,2,3
LPT1,2,3
LPT1,2,3
LPT1,2,3