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3.4.2
Address Specification by Bank Addressing
In address specification by bank addressing, the 16-Mbyte memory space is divided
into 256 64-Kbyte 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 registers 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)
■ Bank Registers and Access Space
Table 3.4-1 lists the access space and main function of each bank register.
Table 3.4-1 Access Space and Main Function of Each Bank Register
Bank register
name
Program bank
Program (PC) space
register (PCB)
Data bank register
Data (DT) space
(DTB)
User stack bank
register (USB)
Stack (SP) space
System stack bank
register (SSB) *1
Additional bank
Additional (AD)
register (ADB)
space
* : The SSB is always used as an interrupt stack.
Access 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 register (CCR:
S) is "1". The USB is used when the stack flag in the
condition register (CCR: S) is "0". *
Data that overflows from the data (DT) space is stored.
Main function
CHAPTER 3 CPU
Initial value
after a reset
FF
H
00
H
00
H
00
H
00
H
35
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