Table 5-13. Parallel Interface; Table 5-14. Parallel Interface - Compaq Deskpro 4000N 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 5-14
lists the parallel registers and associated functions based on mode.
Table 5–14. Parallel Interface Control Registers
Register
Data
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
Base Address:
LPT1 = 378h
LPT2 = 278h
LPT3 = 3BCh
The following paragraphs describe the individual registers. Note that only the LPT1-based
addresses are given in these descriptions.
Data Register, I/O Port 378h
Data written to this register is presented to the data lines D0-D7. A read of this register when in
SPP-compatible mode yields the last byte written. A read while in SPP-extended or ECP mode
yields the status of data lines D0-D7 (i.e., receive data).
In ECP mode in the forward (output) direction, a write to this location places a tagged command
byte into the FIFO and reads have no effect.
5-24 Compaq Deskpro 4000N and 4000S Personal Computers
Table 5-14.
Parallel Interface Control Registers
I/O SPP Mode
Address Ports
Base LPT1,2,3
Base + 1h LPT1,2,3
Base + 2h LPT1,2,3
Base + 3h
Base + 4h
Base + 5h
Base + 6h
Base + 7h
Base + 400h
Base + 400h
Base + 400h
Base + 400h
Base + 401h
Base + 402h
First Edition – September 1997
EPP Mode
Ports
LPT1,2
LPT1,2
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