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CHAPTER 3 CPU AND CONTROL UNITS
3.8.4
Table Base Register (TBR)
Indicate the beginning address of the vector table for EIT.
■ Table Base Register (TBR)
The table base register (TBR) consists of 32 bits as shown below:
Obtain a vector address by adding to the TBR the offset value predetermined for an EIT cause.
The table base register (TBR) is initialized to 000FFC00
■ EIT Vector Table
A 1 KB area from the address indicated in the table base register (TBR) is the vector area for EIT.
The size for each vector is 4 bytes. The relationship between a vector number and a vector
address can be expressed as follows:
vctadr
vctadr: Vector address
vctofs: Vector offset
vct: Vector number
The low-order two bits of the addition result are always handled as 00.
The area from 000FFC00
Special functions are allocated to some of the vectors.
Table 3.8-3 shows the vector table on the architecture.
54
bit 31
TBR
= TBR + vctofs
- 4 × vct)
= TBR + (3FC
H
to 000FFFFF
H
by a reset.
H
is the initial area for the vector table upon reset.
H
0
[Initial value]
000FFC00
H
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