
2.1 CPU
19
s Type of Bank Addressing
In bank addressing the 16-Mbyte memory space is divided into 256 banks of 64 Kbytes each, with bank
addresses maintained in a system of bank registers. There are five types of bank registers available.
Table 2.1.1 lists bank registers, the space accessed by each register, and principal uses.
Table 2.1.1 Spaces Accessed by Bank Registers
To enhance coding efficiency, each instruction has defined default spaces for each type of addressing as
shown in Table 2.1.2. When an addressing operation uses a space other than its default space, a prefix
code corresponding to the desired bank is attached to the beginning of the instruction to allow access to
the bank space designated by that prefix code.
Table 2.1.2 Default Spaces
Bank register
Space name
Principal uses
Initial
value at
reset
Program bank register
(PCB)
Program (PC) space
Storage of instruction codes, vector tables, and
immediate data
FFH
Data bank register (DTB)
Data (DT) space
Storage of readable/writable data
Access to internal or external peripheral resource
control registers and data registers
00H
User stack bank register
(USB)
Stack (SP) space
Area used for stack access to registers for saving
of PUSH/POP instructions and interrupt instruc-
tions, etc.
SSB is used when CCR S=1, USB used when
S=0.
00H
System stack bank register
(SSB)
00H
Additional bank register
(ADB)
Additional (AD)
space
Storage of data overflow from data (DT) space
00H
18/ After reset, DT, SP and AD spaces are located in bank 00 (000000H to 00FFFFH), and PC space is
located in bank FF (FF0000H to FFFFFFH).
Default space
Addressing method
Program space
PC indirect, program access, branching
Data space
Addressing using @RW0, @RW1, @RW4, @RW5; @A, addr16, dir
Stack space
Addressing using PUSHW, POPW, @RW3, @RW7
Additional space
Addressing using @RW2, @RW6