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CHAPTER 3 CPU AND CONTROL UNITS
■ Registers
●
General-purpose registers
Registers R0 to R15 are general-purpose registers. These are used as accumulators for various operations and
memory access pointers.
Of these 16 registers, the registers listed below are intended for special applications, for which some
instructions are enhanced.
R13: Virtual accumulator
R14: Frame pointer
R15: Stack pointer
The initial values of R0 to R14 after a reset are indeterminate. The initial value of R15 is "00000000
(SSP value).
●
PS (Program Status) register
This register holds the program status. It is divided into three parts (registers): ILM, SCR, and CCR.
The undefined bits in the following illustration are all reserved bits. Reading any of these bits always
returns "0".
An attempt to write to this register is ignored.
Bit position → 31
●
CCR (Condition Code Register)
7
–
34
R0
R1
R12
R13
R14
R14
6
5
4
S
I
–
32 bits
AC
FP
SP
20
16
ILM
3
2
1
N
Z
V
C
[Initial value]
XXXX XXXX
H
XXXX XXXX
H
0000 0000
H
10
8 7
SCR
CCR
0
[Initial value]
-00XXXX
B
"
H
0
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