CS89712 datasheet(14/170 Pages) CIRRUS

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CS89712

DS502PP2

net Port register (or set of Ethernet Port registers in

some cases) with an initial non-default value.

2.6.3.2

Reset Configuration Block Header

The header (first word of the block located at EE-

PROM address 00h) specifies the type of EE-

PROM used, if a Reset Configuration block is

present, and if so, how many bytes of configuration

data are stored in the Reset Configuration Block.

2.6.3.3

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 sequential EEPROM, with a 1 (XXXX-XXX1)

indicating non-sequential EEPROM. The Ethernet

port functions with either type of EEPROM. The

Ethernet port will automatically generate sequen-

tial addresses while reading the Reset Configura-

tion Block if a non-sequential EEPROM is used.

2.6.3.4

EEPROM Reset Configuration Block

The read-out of either a binary 101X-XXX0 or

101X-XXX1 from the high byte of the header indi-

cates the presence of configuration data. Any other

readout value terminates initialization from the EE-

PROM. If an EEPROM is attached but not used for

configuration, the high byte of the first word should

be programmed with 00h in order to ensure that the

Ethernet port will not attempt to read configuration

data from the EEPROM.

2.6.3.5

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 config-

uration data in the Reset 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 A104h indicates a non-sequential EEPROM pro-

grammed with a Reset Configuration Block con-

taining 4 bytes of configuration data. This Reset

Configuration Block occupies 6 bytes (3 words) of

EEPROM space (2 bytes for the header and 4 bytes

of configuration data).

2.6.4

Groups of Configuration Data

Configuration data is arranged as groups of words.

Each group contains one or more words of data that

are to be loaded into Ethernet Port registers. The

first word of each group is referred to as the Group

Header. The Group Header indicates the number of

words in the group and the address of the Ethernet

Port register where the first data word in the group

is to be loaded. Any remaining words in the group

are stored in successive Ethernet Port registers.

2.6.4.1

Group Header

Bits F through C of the Group Header specify the

number of words in each group that are to be trans-

ferred to Ethernet Port registers (see Figure 3 for

the format). This value is two less than the total

number of words in the group, including 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).

Bits 8 through 0 of the Group Header specify a 9-

bit Ethernet Port Address. This address defines the

Ethernet Port register that will be loaded with the

first word of configuration data from the group.

Bits B though 9 of the Group Header are forced to

0, restricting the destination address range to the

first 512 bytes of Ethernet Port memory.

2.6.5

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 EE-

PROM address of the checksum value can be deter-

mined by dividing the value stored in the Link Byte

by two.) The checksum value is the 2’s comple-

ment of the 8-bit sum (any carry out of eighth bit is

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