SCD1284 datasheet(77/176 Pages) INTEL

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IEEE 1284-Compatible Parallel Interface Controller — CD1284

Datasheet

Another comparator determines if the next character coming from the DMABUF register and the

character in PFHR1 are identical. Compression begins when the pipeline is full (immediately after

a DMA or CPU write to the DMA buffer) and both comparators show identical characters in their

pipeline stages. This starts the compression process and the character in PFHR1 and the DMA

buffer shift forward. The (same) character in PFHR2 is not loaded into the FIFO, but rather the

RLCR increments to ‘1’.

As long as identical additional characters are loaded into the DMA buffer, the RLCR value

continues to increment and the data in PFHR2 does not move into the FIFO. When the repeated

sequence is finally broken, or the RLCR count reaches 127, the RLCR value transfers into the

FIFO, the RLCR zeros, and the character in PFHR2 transfers into the FIFO. Compression resumes

when both comparators indicate the presence of a string of at least three identical characters.

During intervals between DMA transfers, the last two data characters are held in PFHR1 and

PFHR2.

After the entire block transfer is complete, the CPU must either zero RLEen or ensure that both

DMAen and DMAbufWe are zeros. When either of these conditions is true, the pipeline is released

and data held in PFHR1 and PFHR2 transfers into the FIFO.

The timeout interrupt can be a general timer interrupt in the transmit direction. Unlike the receive

case, when DMAdir is true, the timeout status is immediately set when the timeout is triggered by a

‘0’-to-‘1’ transition of Stale. To use the timeout interrupt, the CPU must load the desired time delay

directly into the SDTCR. When the timer expires, Stale becomes true and the timeout interrupt is

generated.

5.12

CD1284 Parallel Port Overview

5.12.1

Terminology

This document uses the terms ‘master’ and ‘slave’ for the IEEE STD 1284 specification terms

‘host’ and ‘peripheral’ that describe the two sides of a parallel-port interface.

5.12.2

Signal Names

The IEEE STD 1284 specification uses different names for the nine control signals, depending on

the current mode of operation (Table 20). The CD1284 uses fixed names for each of its pins. The

names were selected to represent the most commonly used names of the various protocols. The

CD1284 device operates as a slave only. There are four input-control signals driven by the master-

side device, and five output-control signals driven by the slave-side device. The Parallel Data bus

(PD[7:0]) is bidirectional.

Table 20. Signal Names (Sheet 1 of 2)

Names

Compatibility

Rev. NB

Rev. BT

ECP

EPP

Inputs

A_1284

SLCTIN*

A_1284

nAStrb

HstBsy

AUTOFD*

HstBsy

HstAck

nDStrb

HstClk

STROBE*

HstClk

nWrite

nInit

INIT*

nInit

nRevReq

nInit

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