CS8920A Ver la hoja de datos (PDF) - Cirrus Logic

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CS8920A

Crystal LAN ISA Plug-and-Play Ethernet Controller

Cirrus Logic 

CS8920A

out value terminates initialization from the

EEPROM. If an EEPROM is attached but not

used for configuration, Crystal recommends that

the high byte of the first word be programmed

with 00h in order to ensure that the CS8920A

will not attempt to read configuration data from

the EEPROM.

Setting Plug And Play Support Enabled/dis-

abled: Setting bit four of the high byte of the

header disables the CS8920A’s Plug and Play

support. Clearing this bit leaves Plug and Play

support enabled (default). For example, a value

of 1011-XXXX (X = do not care) for the high

byte disables Plug and Play support while a

value of 1010-XXXX leaves Plug and Play en-

abled.

Determining Number of Bytes in the Reset

Configuration Block: The low byte of the Reset

Configuration Block header is known as the link

byte. The value of the Link Byte represents the

number of bytes of configuration data in the Re-

set Configuration Block. The two bytes used for

the header are excluded when calculating the

Link Byte value.

For example, a Reset Configuration Block

header of A112h indicates a non-sequential

EEPROM programmed with eighteen (12h)

bytes of configuration data. The CS8920A’s

Plug and Play support is enabled. The Reset

Configuration Block occupies twenty bytes (10

words) of EEPROM space (2 bytes for the

header and 18 bytes of configuration data).

Groups of Configuration Data

Configuration data are arranged as groups of

words. Each group contains one or more words

of data that are to be loaded into PacketPage reg-

isters. The first word of each group is referred to

as the Group Header. The Group Header indi-

cates the number of words in the group and the

address of the PacketPage register into which the

first data word in the group is to be loaded. Any

DS238PP2

remaining words in the group are stored in suc-

cessive PacketPage registers.

Group Header: Bits F through C of the Group

Header specify the number of words in each

group that are to be transferred to PacketPage

registers (see Figure 3.1). This value is two less

than the total number of words in the group, in-

cluding the Group Header. For example, if bits F

through C contain 0001, there are three words in

the group (a Group Header and two words of

configuration data).

First Word of a Group of Words

FEDCBA9 8 7 6 5 4 3 2 1 0

00

Number of Words

10-bit PacketPage Address

in Group

Figure 3.1. Group Header

Bits 9 through 0 of the Group Header specify a

10-bit PacketPage Address. This address defines

the PacketPage register that will be loaded with

the first word of configuration data from the

group. Bits B and A of the Group Header are

forced to 0, restricting the destination address

range to the first 1024 bytes of PacketPage mem-

ory.

Figure 3.1 shows the format of the Group

header.

Reset Configuration Block Checksum

A checksum is stored in the high byte position

of the word immediately following the last group

of data in the Reset Configuration Block. (The

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