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SYM53C876/876E Data Manual
2-31
Functional Description
Serial EEPROM Interface
Serial EEPROM
Interface
The SYM53C876 implements an interface
that allows attachment of a serial EEPROM
device to the GPIO0 and GPIO1 pins for each
SCSI function. There are several modes of
operation. These relate to the serial EEPROM
and the Subsystem ID register and Subsystem
Vendor ID register for each SCSI function.
These modes are programmable through the
MAD6 and MAD7 pins which are sampled at
power-up or hard reset.
Mode A Operation
No pulldown on MAD6, no pulldown on
MAD7.In this mode, GPIO0 is the serial data
signal (SDA) and GPIO1 is the serial clock
signal (SCL). Certain data in the serial
EEPROM is automatically loaded into chip
registers at power-up or hard reset.
The format of the serial EEPROM data is
defined in Table 2-6. If the EEPROM is not
present, or the checksum fails, the Subsystem
ID and Subsystem Vendor ID registers read
back all zeros. At power-up or hard reset, only
five bytes are loaded into the chip from loca-
tions 00h through 04h.
The Subsystem ID and Subsystem Vendor ID
registers are read only, in accordance with the
PCI specification, with a default value of all
zeros.
Table 2-6: Mode A Serial EEPROM data
format
Byte
Name
Description
00h
SVID(0)
Subsystem Vendor ID,
LSB. This byte is loaded
into the least significant
byte of the Subsystem
Vendor ID register in the
appropriate PCI configu-
ration space at chip
power-up or hard reset.
Subsystem Vendor ID,
MSB. This byte is loaded
into the most significant
byte of the Subsystem
Vendor ID register in the
appropriate PCI configu-
ration spaces at chip
power-up or hard reset.
Subsystem ID, LSB. This
byte is loaded into the
least significant byte of the
Subsystem ID register in
the appropriate PCI con-
figuration space at chip
power-up or hard reset.
Subsystem ID, MSB. This
byte is loaded into the
most significant byte of
the Subsystem ID register
in the appropriate PCI
configuration space at
chip power-up or hard
reset.
Checksum. This 8-bit
checksum is formed by
adding, bytewise, each
byte contained in loca-
tions 00h-03h to the seed
value 55h, and then taking
the 2’s compliment of the
result.
Reserved.
01h
SVID(1)
02h
SID(0)
03h
SID(1)
04h
CKSUM
05h-
FFh
100h-
EOM
rsv
UD
User Data.