CS8920 datasheet(47/66 Pages) CIRRUS

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AN84REV1

CS8920 Technical Reference Manual

3.4.1 Serial Identifier

The Serial Identifier block is used to isolate

each individual ISA adapter in the system

during the PnP isolation sequence. The

Plug and Play ISA Specification defines the

Serial Identifier as consisting of a 32-bit

Vendor ID in compressed ASCII format

(typically the OEM’s EISA ID), a 32-bit

unique serial number and an 8-bit LFSR

checksum calculated on the Vendor ID and

serial number. Refer to Section 6.1 of the

Plug and Play ISA Specification 1.0a for

more information on the definition of the

Serial Identifier.

The Serial Identifier of each ISA adapter

must be unique. It is the responsibility of

the OEM to ensure that each adapter using

the same Vendor ID (EISA ID) is assigned

a unique serial number.

Note: All adapters using Crystal

Semiconductor’s EISA ID of “CSC” for

bytes 0 and 1 of the Vendor ID must set bit

6 of byte three to a 1 and bit 5 of byte three

to 0 (i. e., byte 3 must be X10X XXXX

where X is a don’t care).

Words 30h to 34h defined above in the

Driver Configuration Block are also used as

the PnP Serial Identifier. Refer to Figure

3.4.1 for an example of the Serial Identifier

Block

3.4.2 Resource Descriptors

Immediately following the Serial Identifier

are a series of data structures describing the

resource requirements of the adapter. The

format of this resource data for a typical

CS8920 ISA adapter is:

1. Plug and Play version number

2. Identifier String (variable length)

3. Logical Device ID

• Resource descriptors (as needed)

• IRQ

• IO Ports

• Memory Descriptor 0

• Memory Descriptor 1

• DMA Channel

4. End Tag

The identifier string is a variable length

string of ASCII characters and is used by

the operating system when reporting

configuration and error messages.

Following the Identifier String is the

Logical Device ID. The Logical Device ID

is used by PnP to identify multiple logical

devices embedded in a single physical ISA

card. However, the CS8920 PnP interface

only supports one logical device.

For logical device 0 (the CS8920), a list of

resource descriptors specify the ISA

resources required by the CS8920 (e.g.

DMA channel, IRQ, etc.) along with

acceptable values for each resource. The

order in which the resource descriptors are

listed is not important. Refer to the CS8920

Data Sheet for the acceptable ISA resources

for the CS8920.

The PnP configuration process will attempt

to reserve and assign available ISA

resources for all resource descriptors

specified in the resource descriptor list,

regardless of whether or not the resource is

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