SCD1284 datasheet(110/176 Pages) INTEL

110 / 176 page

CD1284 — IEEE 1284-Compatible Parallel Interface Controller

110

Datasheet

7.1.6

Modem Interrupt Register

The MIR, PIR, and TIR are used during Poll-mode operation of the CD1284. All three registers

provide the same type of information for each of the three service requests. The functions of

RxIreq, TxIreq, and MdIreq have identical meanings, as do the group Rxbusy, Txbusy, and

Mdbusy and the group Rxunfair, Txunfair, and Mdunfair. The least-significant two bits indicate the

number of the channel requesting service. Bits 4:2 are used internally by the CD1284 to set the

context of the service-acknowledge cycle. See the description of Poll-mode operations in Chapter

5.0 for complete details.

Bit

Description

7:4

User defined.

3:2

Channel X: When these bits are set to the values shown below, the channel number is defined.

1:0

User defined.

Access: Read/Write

8-Bit Hex Address: 69

Default Value: 08

Bit 7Bit 6

Bit 5

Bit 4Bit 3Bit 2Bit 1Bit 0

MdIreq

Mdbusy

Mdunfair

ch[1]

ch[0]

Channel Number

Channel 0

Undefined

Channel 2

Channel 3

Bit

Description

RxIreq, TxIreq, and MdIreq: These bits are set by the internal processor when service is required by a

channel. The bits are a direct reflection of the inverse state of the SVCREQ* pins and they are the active-high

output of the latch that drives the SVCREQ* pins. The bits can be scanned by the host to detect an active

service request. These bits are cleared by the internal processor at the beginning of the service-acknowledge

cycle (hardware-service acknowledge) or by the host software when the Poll-mode cycle is terminated.

Rxbusy, Txbusy, and Mdbusy: These bits are set by the internal processor and they remain set until the end of

the service-acknowledge cycle is indicated by either a write to the EOSRR (hardware-service acknowledge),

or cleared by the host software when the Poll-mode cycle is terminated. These bits signal the current state of

the service-acknowledge cycle. When cleared, the internal processor knows that it can assert another service

request of this type.

SCD1284 Datasheet(PDF) 110 Page - Intel Corporation

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