PC97338 datasheet(123/221 Pages) NSC

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4.0 Parallel Port

4.1

INTRODUCTION

The Parallel Port is a communications device that en-

ables transfer of parallel data bytes between the sys-

tem and an external device. Originally designed to

output data to an external printer, the use of this port

has grown to include additional capabilities such as

bidirectional communications, increased data rates

and additional applications (such as network adap-

tors). Despite additional parallel port capability, back-

ward compatability is maintained to support existing

hardware and software.

4.1.1

The Chip Parallel Port Modes

This parallel interface fully supports the IEEE 1284

standard and EPP 1.7 modes of parallel communica-

tions, in both Legacy or Plug and Play configurations.

It supports two Standard Parallel Port (SPP) modes of

operation for parallel printer ports (as found in the IBM

PC-AT, PS/2 and Centronics systems), two En-

hanced Parallel Port (EPP) modes of operation, and

one Extended Capabilities Port (ECP) mode.

The parallel port output pins are protected against po-

tential damage from connecting an unpowered port to

a powered-up printer.

The functional modes supported by the Chip parallel

port are as follows:

• The Standard Parallel Port (SPP) configuration

supports two operation modes:

— In Compatible SPP mode the port is write-only

(for data). Data transfers are software-con-

trolled, accompanied by status and control

handshake lines.

— In Extended SPP mode, the parallel port be-

comes a read/write port, transferring a full data

byte in both directions.

In these modes, low data rates are achieved (sev-

eral hundred bytes per second).

• The Enhanced Parallel Port (EPP) configuration

supports two modes that offer higher bi-directional

throughput and more efficient hardware-based

handling.

— The EPP revision 1.7 mode has the above ad-

vantages but lacks a comprehensive hand-

shaking scheme to ensure data transfer

integrity between communicating devices with

dissimilar data rates.

The IEEE 1284 standard establishes a widely

accepted handshake and transfer protocol

that ensures transfer data integrity. This stan-

dard is met by all modes in this module except

the EPP revision 1.7 mode.

— EPP revision 1.9 mode offers data transfer en-

hancement, while meeting the IEEE 1284 stan-

dard.

• The Extended Capabilities Port (ECP) mode ex-

tends the port capabilities beyond EPP modes by

adding a bi-directional 16-level FIFO with thresh-

old interrupts, for PIO and DMA operation. In this

mode, the device becomes a hardware state-ma-

chine with highly efficient hardware real-time data

transfer control.

4.1.2

Device Configuration

The functional mode of the parallel port is determined

by setting the appropriate bits in the system configu-

ration registers:

All parallel port functions are enabled by setting bit 0

of the system Function Enable Register (FER) to 1.

SPP is the default mode. In this mode, bit 7 of the PTR

and Extended SPP mode when it is 1.

If bit 0 of the Parallel Port Control Register (PCR) is

set to 1, the device enters EPP mode. Bit 1 of this reg-

isters dictates whether mode 1.7 or 1.9 is active, un-

less the Zero Wait State Enable bit 5 of the Function

Control configuration register (FCR) is set to 1. In this

case, the device is in revision 1.7 mode, regardless of

the value of bit 1 of the PCR register.

When bit 2 of the PCR is set to 1, ECP mode is en-

abled.

The parallel port supports plug and play operation; its

interrupt can be routed on one of the following ISA in-

terrupts: IRQ7-IRQ3, IRQ12-IRQ9 or IRQ15 (see

PNP0 register); its DMA signals can be routed to one

of three 8-bit ISA DMA channels (see PNP2 register);

and its base address is software configurable (see

PBAL and PBAH registers)

4.2

STANDARD PARALLEL PORT

MODES

The two Standard Parallel Port (SPP) modes Com-

patible SPP and Extended SPP modes.

Compatible SPP mode is a data write-only mode that

outputs data to a parallel printer, using handshake

bits, under software control.

In Extended SPP mode, parallel data transfer is bi-di-

rectional.

The list of output signals for the standard 25-pin, D-

type connector appears in Table 72 on page 145.

The reset states for handshake output pins in this

mode are listed below in Table 62.

A single Data Register DTR is used for data input and

output (see Section 4.2.3). The direction of data flow

is determined by the system setting in bit 5 of the Con-

trol Register CTR.

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