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CHAPTER 3 CPU
3.7.9
Bank Registers (PCB, DTB, USB, SSB, ADB)
Bank registers specify the highest 8-bit address by bank addressing. The five bank
registers 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)
The PCB, DTB, USB, SSB and ADB registers indicate the individual memory banks
where the program space, data space, user stack space, system stack space and
additional space are located.
■ Bank Registers (PCB, DTB, USB, SSB, ADB)
●
Program bank register (PCB)
The PCB is a bank register that specifies the program (PC) space.
The PCB is rewritten when a software interrupt instruction is executed, when the JMPP, CALLP, RETP
and RETI instructions that branch anywhere within the 16-megabyte space are executed, or when a
hardware interrupt or exception occurs.
●
Data bank register (DTB)
The DTB is a bank register that specifies the data (DT) space.
●
User stack bank register (USB), system stack bank register (SSB)
The USB and SSB are bank registers that specify the stack (SP) space. Whether the USB or the SSB is
used depends on the S flag value in the processor status (PS: CCR). See "3.7.2 Stack Pointers (USP, SSP)",
for details.
●
Additional bank register (ADB)
The ADB is a bank register that specifies the additional (AD) space.
●
Bank setting and data access
All bank registers are byte length. The PCB is initialized to FF
initialized to 00
The other bank registers can be read and written to.
Note:
The MB90460/465 series supports up to the memory space contained in the device.
See "3.4.2 Address Specification by Bank Addressing", for the operation of each register.
54
by a reset. The PCB can be read, but cannot be written to.
H
by a reset. The other bank registers are
H
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