CS8920 datasheet(38/66 Pages) CIRRUS

38 / 66 page

AN84REV1

CS8920 Technical Reference Manual

high byte of the word (bits 15-8). The

checksum value is the 2’s complement of

all the bytes in the Reset Configuration

Block excluding the checksum byte. (The

low byte of the checksum word is not used

and it is recommended that it be set to

0x00.) Since the checksum is the 2’s

complement of all the bytes in the Reset

Configuration Block, a total sum of 0

should result when the checksum value is

added to the sum of all the preceding bytes.

3.2.2 Typical Reset Blocks

The contents of the Reset Configuration

Block depend on the CS8920’s intended

mode of operation and adapter

configuration. Following are examples of

typical Reset Configuration Blocks for

three different modes of operation: as a

legacy adapter, as a PnP adapter, and as a

PnP adapter with the Auto-wakeup feature

enabled.

3.2.2.1 Recommended Reset

Configuration Block for a Legacy

Adapter

Table 3.2 shows the recommended Reset

Configuration Block for a CS8920 adapter

installed in a legacy system. The definition

of a legacy system as used in this chapter is

any PC system that does not rely on a

function of PnP to automatically configure

and activate the adapter.

The default state of the CS8920 after an

ISA reset is inactive with its IO base

address set to 0x00. Therefore, the adapter

must be activated and the IO base address

set from the EEPROM after each ISA reset.

Note: In systems that have an

autoconfiguring PnP BIOS but an ESCD

database is not maintained or the BIOS

does not activate the adapter, it will be

necessary to manually configure the

CS8920 as if in a legacy system. However,

it may still be advantageous to leave the

PnP functions of the CS8920 enabled.

Addr

Word

Description

00h

B112h

PnP Disabled, 18 bytes follow

01h

2158h

3 words, start with PacketPage 158h (IA)

02h

0100h

Individual Address

03h

0302h

04h

0504h

000102030405h

05h

0360h

1 word to PacketPage 360h (IO Base)

06h

0003h

IO Base Address = 300h

07h

0330h

1 word to PacketPage 330h (RegActivate)

08h

0001h

Activate Adapter

09h

2B00h

Checksum of 20 bytes

Table 3.1. Reset Configuration Block

for Legacy System

This will allow the PnP BIOS or other

autoconfiguring components to be aware of

the CS8920 installed in the system and the

resources used by it. This will help insure

other PnP devices are not assigned

resources used by the CS8920. See section

3.4 for a discussion on manually

configuring the CS8920 using the PnP

resource tree.

CS8920 Datasheet(PDF) 38 Page - Cirrus Logic

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