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CHAPTER 2 CPU
MB90560 series
2.4
2.4.2 Bank addressing
Addressing
In bank addressing, the 16-megabyte memory space is divided into 256 64-kilobyte
banks. A bank address that corresponds to each space is specified in the bank register
to determine the upper 8 bits of the address. The lower 16 bits of the address are
specified by the instruction.
The five types of bank register classified by function are as follows:
Program bank register (PCB)
Data bank register (DTB)
User stack bank register (USB)
System stack bank register (SSB)
Additional bank register (ADB)
I
Bank registers and access space
Table 2.4-1 lists the access space and main function of each bank register.
Table 2.4-1 Access space and main function of each bank register
*1 The SSB is always used as an interrupt stack.
Figure 2.4-4 shows the relationship between the memory space divisions and each register.
See Section 2.7.9, "Bank registers (PCB, DTB, USB, SSB, ADB)," for details.
Bank register
name
Access
space
Main function
Initial value
after a reset
Program bank
register (PCB)
Data bank regis-
ter (DTB)
User stack bank
register (USB)
System stack
bank register
(SSB) (*1)
Additional bank
register (ADB)
Program
(PC) space
Data (DT)
space
Instruction codes, vector tables, and immediate-value data
are stored.
Read/write data is stored. Internal or external peripheral
control registers and data registers are accessed.
This area is used for stack accesses such as when PUSH/
POP instructions and interrupt registers are saved. The
SSB is used when the stack flag in the condition code reg-
ister (CCR:S) is 1. The USB is used when the stack flag in
the condition code register (CCR:S) is 0. (*1)
FF
H
00
H
Stack (SP)
space
00
H
00
H
Additional
(AD) space
Data that overflows from the data (DT) space is stored.
00
H