SCD1284 datasheet(142/176 Pages) INTEL

142 / 176 page

CD1284 — IEEE 1284-Compatible Parallel Interface Controller

142

Datasheet

The PFEP is cleared by a device or FIFO reset.

7.7.10

Parallel FIFO Fill Pointer Register

This register holds the internal fill location pointer of the FIFO. It identifies the location in the

FIFO to receive the next data byte from the pipeline.

The PFFP is cleared by a device or FIFO reset.

7.7.11

Parallel FIFO Holding Register 1

7.7.12

Parallel FIFO Holding Register 2

These two 1-byte registers provide a data pipeline between the FIFO and DMA buffer. Data always

flows into PFHR1 first, then to PFHR2, and finally, either to the FIFO or the DMABUF register.

The flow is to the FIFO if DMAdir is ‘1’ and, from the FIFO if DMAdir is ‘0’. The pipeline and the

holding registers support ‘tagged’ data for complete support of ECP Parallel Port mode. Tagged

data is either an address or a run-length code.

If RLEen (PFCR[3]) is set, in the receive direction, run-length codes are captured in the RLCR for

decompression of received data. ECP address codes are recognized and pass into the PFHR1–

PFHR2 pipeline. The presence of an ECP address interrupts DMA flow and causes an interrupt to

the host so it can remove the tagged data from the pipeline by reading either PFHR2 or PFHR1.

In the transmit direction, the host can introduce ECP address (tagged) data or run-length codes for

precompressed data by setting the SetTAG bit (PFCR[2]) and writing the byte to be tagged to

PFHR1. For each tagged data transfer, the SetTAG bit must be set prior to writing to PFHR1. To

perform a tagged data transfer, the automatic DMA function must be disabled prior to the transfer

(set DMAen

= 0). This can be done at the same time that SetTAG is set to ‘1’.

Access: Read/Write

8-Bit Hex Address: 38

Default Value: 00

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

6-bit binary FIFO Pointer Value

Access: Read/Write

8-Bit Hex Address: 35

Default Value: 00

Bit 7Bit 6Bit 5Bit 4Bit 3

Bit 2Bit 1

Bit 0

8-bit Character Data

Access: Read/Write

8-Bit Hex Address: 36

Default Value: 00

Bit 7Bit 6Bit 5Bit 4Bit 3

Bit 2Bit 1

Bit 0

8-bit Character Data

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