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CS8920A

Crystal LAN ISA Plug-and-Play Ethernet Controller

Cirrus Logic 

CS8920A

Reset Configuration Block

The first block in EEPROM, referred to as the

Reset Configuration Block, is used to automat-

ically program the CS8920A with an initial

configuration after a reset. It is a block of con-

tiguous 16-bit words starting at EEPROM

address 00h. The Reset Configuration Block can

be divided into three logical sections: a header,

one or more groups of configuration data words,

and a checksum value. All of the words in the

Reset Configuration Block are read sequentially

by the CS8920A after each reset, starting with

the header and ending with the checksum. Each

group of configuration data is used to program a

PacketPage register (or set of PacketPage regis-

ters in some cases) with an initial non-default

value.

Reset Configuration Block Header: The header

(first word of the block located at EEPROM ad-

dress 00h) specifies the type of EEPROM used,

whether or not a Reset Configuration block is

present, if the CS8920A’s Plug and Play support

is enabled or disabled, and how many bytes of

data are stored in the Reset Configuration Block.

Determining the EEPROM Type: The LSB of

the high byte of the header indicates the type of

EEPROM attached: sequential or non-sequential.

An LSB of 0 (XXXX-XXX0) indicates a se-

quential EEPROM. An LSB of 1 (XXXX-

XXX1) indicates a non-sequential EEPROM.

The CS8920A works equally well with either

type of EEPROM. The CS8920A will automat-

ically generate sequential addresses while

reading the Reset Configuration Block if a non-

sequential EEPROM is used.

Checking EEPROM for presence of Reset Con-

figuration Block: The readout of either a binary

101X-XXX0 or 101X-XXX1 (X = do not care)

from the high byte of the header indicates the

presence of configuration data. Any other read-

Word Address

Value

FIRST WORD in DATA BLOCK

00h

B112h

FIRST GROUP of WORDS

01h

2158h

02h

0100h

03h

0302h

04h

0504h

SECOND GROUP of WORDS

05h

0360h

06h

0003h

THIRD GROUP of WORDS

07h

0330h

08h

CHECKSUM Value

09h

0001

1B00h

Description

Configuration Block Header.

The high byte, B1h, indicates a ’C56 EEPROM (non-sequential) is attached

and Plug and Play is disabled. The Link Byte, 12h, indicates the number of

bytes of configuration data in this block.

Group Header for first group of words.

Three words to be loaded, beginning at 0158h in PacketPage memory.

Individual address, bits[39-32], bits[47-40]

Individual address, bits[23-16], bits[31-24]

Individual address, bits[7-0], bits[15-8]

Group Header for second group of words.

One word to be loaded at 360h in PacketPage memory.

IO Base address = 300h

Group Header for third group of words.

One word to be loaded at 330h in PacketPage memory.

Set adapter’s activate bit (make active on reset w/o PnP).

The high byte, 1Bh, is the checksum value. The checksum includes word

addresses 00h through 08h. The hexadecimal sum of the bytes is E5h,

resulting in a 2’s complement of 1Bh. The low byte, 00h, provides a pad to

the word boundary.

Table 3.6. EEPROM Configuration Block Example

20

DS238PP2

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