MB95120MB Series
2. Register
The MB95120MB series has two types of registers; dedicated registers in the CPU and general-purpose registers
in the memory. The dedicated registers are as follows:
Program counter (PC)
: A 16-bit register to indicate locations where instructions are stored.
Accumulator (A)
: A 16-bit register for temporary storage of arithmetic operations. In the case of
an 8-bit data processing instruction, the lower 1 byte is used.
Temporary accumulator (T) : A 16-bit register which performs arithmetic operations with the accumulator.
In the case of an 8-bit data processing instruction, the lower 1 byte is used.
Index register (IX)
Extra pointer (EP)
Stack pointer (SP)
Program status (PS)
: A 16-bit register for index modification
: A 16-bit pointer to point to a memory address.
: A 16-bit register to indicate a stack area.
: A 16-bit register for storing a register bank pointer, a direct bank pointer, and
a condition code register
Initial Value
16-bit
FFFDH
0000H
0000H
0000H
0000H
0000H
0030H
: Program counter
: Accumulator
PC
AH
TH
AL
TL
: Temporary accumulator
: Index register
IX
: Extra pointer
EP
SP
PS
: Stack pointer
: Program status
The PS can further be divided into higher 8 bits for use as a register bank pointer (RP) and a direct bank pointer
(DP) and the lower 8 bits for use as a condition code register (CCR) . (Refer to the diagram below.)
• Structure of the program status
bit 15 bit 14 bit 13 bit 12 bit 11 bit 10 bit 9 bit 8 bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0
R4
R3
R2
R1
R0 DP2 DP1 DP0
H
I
IL1
IL0
N
Z
PS
C
V
RP
DP
CCR
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