CS8920 datasheet(36/66 Pages) CIRRUS

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AN84REV1

CS8920 Technical Reference Manual

3.0 EEPROM-based Configuration

The CS8920 and media access control

(MAC) driver obtain configuration data

from a serial EEPROM connected via the

CS8920’s serial interface. This eliminates

the need for configuration jumpers or

switches on the ISA adapter or

motherboard.

3.1 Format of Configuration Data

Three types of configuration data are stored

in the EEPROM: configuration data

automatically loaded into the CS8920 after

each reset, configuration data used by the

MAC driver, and Plug and Play (PnP)

resource data.

00h

1Bh

Reset Configuration Block

1Ch

34h

Driver Configuration Block

35h

7Fh

PnP Resource Data

Figure 3.1 EEPROM Data Blocks

Each type of configuration data is grouped

together, organized as 16-bit words, in a

separate block of the EEPROM. The

arrangement and location of the three

blocks of configuration data are shown in

Figure 3.1.

3.2 Reset Configuration Block

After each reset (except EEPROM reset)

the CS8920 checks to see if an EEPROM is

connected. If an EEPROM is present, the

CS8920 automatically loads first block of

data stored in the EEPROM into its internal

registers. This block of data is referred to

as the Reset Configuration Block. It is

used to initialize the CS8920 after each

reset. If an EEPROM is not present (or a

checksum error indicates the Reset

Configuration Block is invalid) the CS8920

executes an EEPROM reset causing all

PacketPage registers to be loaded with their

default values.

Note: The default state of the CS8920

after an EEPROM reset is inactive (i.e., all

normal ISA bus IO to or from the CS8920

is disabled). Communication with the

CS8920 must then be established using the

Crystal auxiliary key written to the CS8920

via the PnP write-data port. Refer to

Section 3.5 for more information on using

the CS8920 auxiliary key and its use in

programming and initializing the

EEPROM.

3.2.1 Reset Configuration Block Format

The Reset Configuration Block must begin

at EEPROM word address 0x00 and can

vary in length up to a maximum of 28

words (word address 0x1B).

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