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CS8920A

Crystal LAN ISA Plug-and-Play Ethernet Controller

Cirrus Logic 

CS8920A

• A reset signal on the system bus places all

Plug and Play cards into a mode in which

they are all waiting for configuration to be-

gin.

• A special key is written to all all of the PNP

cards to initialize them for selection.

• A special series of reads is performed that

allows a single card to be selected. The se-

lected card is given a system identifier, called

the card select number (CSN). The configu-

ration software then determines the resource

requirements of the card. Finally, the selected

card is placed into a sleep mode. The remain-

ing cards are individually selected and

assigned a CSN and their resource needs de-

termined.

• The configuration software then selects an

individual card using the CSN, assigns non-

conflicting resources to the card, and then

enables the card for normal operation. This is

repeated for each of the Plug and Play cards

until all of the cards have been configured

and enabled.

Plug and Play Auxiliary Key

The CS8920A will respond to a special auxiliary

key at any time. The auxiliary initiation key is

normally used for testing/debug purposes. Two

bytes of 00 should proceed the initiation or aux-

iliary key. This auxiliary initiation key is listed

below in hexadecimal:

6A, B5, DA, 6D, B6, 5B, 2D, 16

0B, 05, 02, 01, 80, C0, 60, 30

18, 0C, 06, 83, 41, 20, 90, 48

24, 12, 89, C4, E2, F1, F8, FC

Plug and Play Device IDs

The Plug and Play device ID is a unique identi-

fier that is used by the operating system to

associate the Plug and Play card with its device

DS238PP2

CS8920A Pin

(Pin #)

EECS

(Pin 141)

EESK

(Pin 142)

EEDO

(Pin 6)

EEDI

(Pin 7)

CS8920A Function

EEPROM Chip

Select

1 MHz EEPROM Serial

Clock output

EEPROM Data Out

(data to EEPROM)

EEPROM Data In (data

from EEPROM)

EEPROM

Pin

Chip Select

Clock

Data In

Data Out

Table 3.5. EEPROM Interface

driver. Microsoft administers the assignment of

these device IDs. Contact Microsoft to receive a

unique device ID.

3.5 Configuration with EEPROM

EEPROM Interface

The interface to the EEPROM consists of the

four signals shown in Table 3.5

EEPROM Memory Organization

EEPROM is used to store initial configuration

information for the CS8920A. The EEPROM is

organized in one or more blocks of 16-bit words.

The first block in EEPROM, referred to as the

Configuration Block, is used to configure the

CS8920A after reset. An example of a typical

Configuration Block is shown in Table 3.6 . Ad-

ditional user data may also be stored in the

EEPROM if space is available. The additional

data are stored as 16-bit words and can occupy

any EEPROM address space beginning immedi-

ately after the end of the Reset Configuration

Block up to address 7Fh, depending on

EEPROM size. This additional data can only be

accessed through software control (refer to Sec-

tion 3.6 for more information on accessing the

EEPROM). Address space 80h to AFh is re-

served

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