SCD1284 datasheet(152/176 Pages) INTEL

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CD1284 — IEEE 1284-Compatible Parallel Interface Controller

152

Datasheet

7.8.12

Special Command Register

This register provides the peripheral host processor to issue special commands to the channel

control state-machine. In response, the state-machine will perform the indicated IEEE STD 1284-

defined handshake on the parallel interface.

Bit

Description

7:5

Mode Control: These three bits control the type of transfer desired and whether or not it is enabled to do so.

The ManMd bit selects Manual mode, which allows the user direct control over all parallel data and parallel

port control signals. MMDir controls the direction of the MDR (Manual Data register), and ManOE is the output

enable when MMDir

= 1 (output mode).

E1284 allows the parallel port to engage in IEEE 1284 negotiations; ETxfr enables data transfers. The ETxfr

enable is only used for data transfers. EPP address read and write functions do not require that the ETxfr bit

be set.

Ig_SEL: This bit prevents the CD1284 from considering the state of the SLCTIN* input when deciding

whether or not to accept Compatibility mode forward data transfers.

When Ig_SEL is reset, SLCTIN* must be active (low) to receive data on the parallel port in response to a

STROBE* input. If Ig_SEL is set, SLCTIN* is not considered and data is accepted regardless of its state. The

Ig_SEL bit should be set/reset together with the E1284 bit.

3:2

Host Timer Test Control [1:0]: These two bits control the clock rate of the host timeout timer and are

intended primarily for manufacturing test purposes. As such, normal user-level programming should leave

these bits cleared (‘0’). When these bits are set to ‘1’, the timer is completely disabled – useful for factory

debug purposes.

1:0

Manual Mode Control: These two bits provide direction and output enable manual control over the parallel

port.

Access: R/W

8-Bit Hex Address: 2A

Default Value: 00

Bit 7Bit 6

Bit 5

Bit 4Bit 3Bit 2Bit 1Bit 0

TestMux

ClrPs

SetPs

EPIrq

RevRq

ManMd

E1284

Etxfr

Mode

Compatibility mode; transfers disabled.

Compatibility mode; transfers enabled.

IEEE 1284 negotiation; transfers disabled.

IEEE 1284 negotiation; transfers enabled.

Manual mode.

MMDir

ManOE

Mode

Reverse direction.

Forward direction disabled.

Forward direction enabled.

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