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2-62
Functional Description
needed. For example, to connect to a 64 Kbytes external ROM use a
pull-up on MAD[2]. If the external memory interface is not used,
MAD[3:1] should be pulled high.
The SYM53C1010 allows the system to determine the size of the
available external memory using the
Expansion ROM Base Address
(ERBA)
register in the PCI configuration space. For more information on
how this works, refer to the PCI specification or the Expansion ROM
Base Address register description in
Chapter 4, “Registers”
.
MAD[0] is the slow ROM pin. When pulled up it enables two extra clock
cycles of data access time to allow use of slower memory devices. The
external memory interface also supports updates to flash memory.
2.4 Serial EEPROM Interface
For each SCSI function, the SYM53C1010 implements an interface
permitting attachment of a serial EEPROM device to the GPIO[0] and
GPIO[1] pins. There are two modes of operation relating to the serial
EEPROM, the
Subsystem ID (SID)
register, and the
Subsystem Vendor
ID (SVID)
register for each SCSI function. These modes are
programmable through the MAD[7] pin, which is sampled at power-up.
2.4.1 Default Download Mode
In this mode, MAD[7] is pulled down internally, GPIO[0] is the serial data
signal (SDA) and GPIO[1] is the serial clock signal (SCL). Certain data
in the serial EEPROM is automatically loaded into chip registers at
power-up.
The format of the serial EEPROM data is defined in
Table 2.7
. If the
download is enabled and an EEPROM is not present or the checksum
fails, the
Subsystem ID (SID)
and
Subsystem Vendor ID (SVID)
registers
read back all zeros. At power-up, five bytes are loaded into the chip from
locations 0xFB through 0xFF.
The Subsystem ID and Subsystem Vendor ID registers are read only in
accordance with the PCI specification, with a default value of all zeros if
the download fails.
Note:
The speed of the serial EEPROM must be 400 Kbits/s.