Technical data

System ROM, Continued
System ROM
Part Format
Table 2–4 shows the part formats in the system ROM.
Table 2–4 System ROM Part Formats
Byte Name Description
Word 02h Version Contains the low 8 bits of
the version number of the
console code for the Model
90 system firmware.
03h ROM byte number Indicates the position of
the byte among the set of
ROMs used to implement
the firmware. This value is
equal to the low 2 bits of the
physical address of the first
byte in the ROM part. The
value ranges from 0 to 3.
04h to 06h Manufacturing
check data
Used for a quick check of
the ROM. The data are 55h,
AAh, and 33h.
07h ROM part length Indicates the length of the
ROM part divided by the
data path width in bytes.
Last byte Checksum For each ROM byte contains
a simple 8-bit add and rotate
checksum. In a 16-bit ROM
the last two bytes contain
a checksum, one checksum
for each byte address in the
device.
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