Crystal LAN CS8920, Technical Reference Manual, Page: 37 / 67

AN84REV1 37
CS8920 Technical Reference Manual
3.2.1.1 Reset Configuration Block
Header
The word at EEPROM address 0x00 is the
Reset Configuration Block header. The
header indicates the type of EEPROM in
use and the length of the Reset
Configuration Block (the number of bytes
loaded into the CS8920 after reset). It can
also be used to disable the PnP feature of
the CS8920.
The presence of bit patterns 1010b (0xA) or
1011b (0xB) in bits 15-12 of the header
indicate the presence of a Reset
Configuration Block. The plug and play
circuitry of the CS8920 can be disabled by
setting bits 15-12 (high nibble) of the
header to 0xB.
Bit 8 (bit 0 being the LSB of the word) of
the header specifies the type of EEPROM
used. A value of 0 in bit 8 indicates a
sequential EEPROM is used. A value of 1
in bit 8 indicates a non-sequential
EEPROM is used. (The CS8920 works
equally well with either type of EEPROM.
It will automatically generate sequential
addresses while reading the Reset
Configuration Block from non-sequential
type EEPROMs.)
The low byte of the header (bits 7-0)
specify the number of bytes of
configuration data in the Reset
Configuration Block including the first
word and checksum at the end of the block.
Example: a Reset Configuration Block of
0xA10A indicates a valid configuration
block, non-sequential EEPROM, 10 bytes
of configuration data follow, and PnP is
enabled.
3.2.1.2 Configuration Data
Following the Reset Configuration Block
header are one or more groups of
configuration data that are to be
automatically loaded into the CS8920’s
PacketPage registers.
Each group of configuration data consists
of a group header (the first word in the
group) and one or more words of
configuration data. The group header
indicates the number of words in the group
along with the address of the PacketPage
register into which the first word of
configuration data are to be loaded.
The value in bits 15-12 of the group header
is one less than the total number of
configuration data words in the group. For
example, if bits 15-12 equal 0001, there are
two words of configuration data in the
group.
Bits 9 through 0 of the group header
indicate the 10-bit address of the
PacketPage register the first word of
configuration data in the group is to be
loaded into. If there are additional
configuration data words in the group, they
are loaded in successive PacketPage
registers. See Table 3.1 for an example.
Bits 11 and 10 of the group header are
forced to 0 when read by the CS8920,
restricting the destination address range of
the configuration to the first 1024 bytes of
the PacketPage memory.
3.2.1.3 Checksum
The last word of the Reset Configuration
Block contains an 8-bit checksum in the