
SYM53C876/876E Data Manual
4-9
Registers
PCI Configuration Registers
Register 18h
Base Address Two (Memory)
Read/Write
This register has bit zero hardwired to zero. The
other bits are used to map the 4 KB SCRIPTS
RAM into memory space. This register is enabled
only if the internal SCRIPTS RAM is enabled.
The internal SCRIPTS RAM is disabled by con-
necting a 4.7 K
resistor between MAD5 and
ground, which is sensed immediately after a chip
reset. SCRIPTS RAM is also disabled by setting
the Enable Memory Space bit to zero in the SCSI
PCI Configuration Command register, bit 1.
If MAD5 is left unconnected, an internal pull-up
enables the SCRIPTS RAM and this Base
Address register.
If enabled, as with all Base Address registers, ini-
tialize this Base Address register to a value that
does not conflict with other memory resources.
Otherwise, memory conflicts may occur.
For detailed information on the operation of this
register, refer to the PCI specification.
Register 2Ch
Subsystem Vendor ID
Read Only
This register uniquely identifies the vendor manu-
facturing the add-in board or subsystem where
this PCI device resides. It provides a mechanism
for an add-in card vendor to distinguish its cards
from another vendor’s cards, even if the cards
have the same PCI controller installed on them
(and therefore the same Vendor ID and Device
ID). This register loads automatically at powerup
from an external serial EEPROM if in operating
mode A and the load from EEPROM is success-
ful. The 16-bit value that should be stored in the
external serial EEPROM for this register is the
vendor’s PCI Vendor ID and must be obtained
from the PCI Special Interest Group (SIG). If in
operating mode D, this register is loaded with a
default value of 1000h. If an error occurs during a
load from EEPROM or if the operating mode is
B, this register defaults to a value of 0000h. See
the
Serial EEPROM Interface
section in Chapter 2
for information about the values to load in this
register.
BAT
31-28
Default >>>
X
BAT
27-24
BAT
23-20
BAT
19-16
BAT
15-12
BAT
11-8
BAT
7-4
BAT
3-0
X
X
X
X
X
X
XXX0
SVID
15-12
SVID
11-8
SVID
7-4
SVID
3-0
If EEPROM not enabled <<<Default>>> Mode A
0
If EEPROM not enabled <<<Default>>> Mode D
1
EEPROM value if EEPROM enabled <<<Default>>>
X
0
0
0
0
0
0
X
X
X