ROM Memory
Overview
The system board ROM contains processor restart, diagnostic and
console code, and the primary bootstrap program. Another small
ROM is uniquely programmed for each system with its network
address.
System Board
ROM
The system board ROM contains four 128 KB x 8 FLASH ROM
chips that collectively hold 512 KB of data. ROM data appears at
physical addresses 2004.0000 through 200B.FFFF. The data path
to this ROM is 32 bits wide. Certain physical addresses in the
ROM have fixed uses. These fixed uses are listed in Table 1–5.
Table 1–5 ROM Fixed Uses
2004.0000
Processor restart address. The processor begins
execution at this address in non-mapped mode
when a processor restart occurs.
2004.0004
System type register SYS_TYPE. The contents of
this longword supplement the internal processor
SID register to identify the processor and system
type.
Network
Address ROM
A 32-byte ROM on the system board contains a unique network
address for each system. Data from this ROM is read in the
low-order bytes of 32 consecutive longwords at physical addresses
2780.0000 through 2780.007C. The network address occupies the
first six bytes (addresses 2780.0000 through 2780.0014). The byte
at 2780.0000 is the first byte to be transmitted or received in an
address field of an Ethernet packet. Its low-order bit (bit 0) is
transmitted or received first in the serial bit stream.
This ROM is installed in a socket so it can be moved in the event
that a system board is replaced.
1–25
