Input/Output Interfaces

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

 

 

SPP

EPP

ECP

I/O

 

Mode

Mode

Mode

Address

Register

Ports

Ports

Ports

 

 

 

 

 

Base

Data

LPT1,2,3

LPT1,2

LPT1,2,3

 

 

 

 

 

Base + 1h

Printer Status

LPT1,2,3

LPT1,2

LPT1,2,3

 

 

 

 

 

Base + 2h

Control

LPT1,2,3

LPT1,2

LPT1,2,3

 

 

 

 

 

Base + 3h

Address

--

LPT1,2

--

 

 

 

 

 

Base + 4h

Data Port 0

--

LPT1,2

--

 

 

 

 

 

Base + 5h

Data Port 1

--

LPT1,2

--

 

 

 

 

 

Base + 6h

Data Port 2

--

LPT1,2

--

 

 

 

 

 

Base + 7h

Data Port 3

--

LPT1,2

--

 

 

 

 

 

Base + 400h

Parallel Data FIFO

--

--

LPT1,2,3

 

 

 

 

 

Base + 400h

ECP Data FIFO

--

--

LPT1,2,3

 

 

 

 

 

Base + 400h

Test FIFO

--

--

LPT1,2,3

 

 

 

 

 

Base + 400h

Configuration Register A

--

--

LPT1,2,3

 

 

 

 

 

Base + 401h

Configuration Register B

--

--

LPT1,2,3

 

 

 

 

 

Base + 402h

Extended Control Register

--

--

LPT1,2,3

Base Address:

LPT1 = 378h

LPT2 = 278h

LPT3 = 3BCh

 

Technical Reference Guide

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5-13