SCD1284 datasheet(146/176 Pages) INTEL

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CD1284 — IEEE 1284-Compatible Parallel Interface Controller

146

Datasheet

The SDTPR is cleared by a device reset.

7.8

Channel Registers — Parallel Port

7.8.1

EPP Address Register

This register is only used during EPP mode.

The CD1284 deposits the value obtained during an EPP address write command in this register.

The CD1284 provides this value in response to an EPP address read command.

7.8.2

Host Timeout Value Register

This register holds the 8-bit value used to set the Host timeout period. The HTVR is an unsigned,

binary value. The reset state of this register is ‘0xFF’.

A function missing in Revision C and earlier devices is an on-chip timer to indicate that the remote

host has not responded in a specified time period. The Host timeout is defined in the IEEE STD

1284 specification as a period of one second.

Revision D and newer devices add a user-programmable timer to provide a timeout if the remote

host does not respond to specific parallel port transactions. The timer is started by the parallel port

state machine each time it starts a sequence requiring a host response. Activation of the timer is

automatic and an interrupt is generated to the local host CPU if the timer expires before the remote

host responds.

Note:

Users familiar with the IEEE specification note that the events that start the timer cause the

peripheral device to wait for a remote host-generated event. For example, during the negotiation

sequence after event 2, the peripheral waits for event 3 – a host-generated event. If the host does

not respond and moves the negotiation sequence to event 4 within one second, the peripheral enters

the ‘host timeout’ condition.

The timer is a 14-bit counter clocked by the system clock (CLK) prescaled (divided) by 2048. Then

the 8-bit HTVR (address offset 0x24) is programmed and compared with the most-significant 8 bits

of the 14-bit counter. Each time the parallel port executes an event requiring a host response, the

Access: Read/Write

8-Bit Hex Address: 25

Default Value: 00

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

8-bit Binary Value

Access: Read/Write

8-Bit Hex Address: 24

Default Value: FF

Bit 7Bit 6Bit 5Bit 4Bit 3

Bit 2Bit 1

Bit 0

HTVR[7]

HTVR[6]

HTVR[5]

HTVR[4]

HTVR[3]

HTVR[2]

HTVR[1]

HTVR[0]

SCD1284 Datasheet(PDF) 146 Page - Intel Corporation

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