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CHAPTER 2 CPU
2.3.2 Special Registers
The special registers are used for special purposes. They are the program counter
(PC), program status (PS), table base register (TBR), return pointer (RP), system stack
pointer (SSP), user stack pointer (USP), and multiplication/division result register
(MDH/MDL).
■
Special Registers
Figure 2.3.4 shows the configuration of special registers.
Figure 2.3-4 Configuration of Special Registers
❍
Program counter (PC)
The program counter indicates the address of the program being executed.
Bit 0 is set to 0 when the PC is updated according to instruction execution. Bit 0 may be set to 1
only when an odd-numbered address is specified for the branch destination address. Even at
this event, bit 0 is invalid and an instruction must be put at an address consisting of a multiple of
two.
The initial value after resetting is undefined.
XXXX XXXX
H
XXXX XXXX
H
0000 0000
H
000F FC00
H
XXXX XXXX
H
XXXX XXXX
H
XXXX XXXX
H
PC
PS
TBR
RP
SSP
USP
MDH
MDL
Program counter
Program status
Table base register
Return pointer
System stack pointer
User stack pointer
Multiplication/division
result register
[Initial value]
(undefined)
(undefined)
(undefined)
(undefined)
(undefined)