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21
MB89650AR Series
2. Registers
The F
2
MC-8L family has two types of registers; dedicated registers in the CPU and general-purpose registers
in the memory. The following dedicated registers are provided:
Program counter (PC):
A 16-bit register for indicating instruction storage positions
Accumulator (A):
A 16-bit temporary register for storing arithmetic operations, etc. When the
instruction is an 8-bit data processing instruction, the lower byte is used.
Temporary accumulator (T): A 16-bit register which performs arithmetic operations with the accumulator
When the instruction is an 8-bit data processing instruction, the lower byte is used.
Index register (IX):
A 16-bit register for index modification
Extra pointer (EP):
A 16-bit pointer for indicating a memory address
Stack pointer (SP):
A 16-bit register for indicating a stack area
Program status (PS):
A 16-bit register for storing a register pointer, a condition code
The PS can further be divided into higher 8 bits for use as a register bank pointer (RP) and the lower 8 bits for
use as a condition code register (CCR). (See the diagram below.)
PC
A
T
IX
EP
SP
PS
16 bits
: Program counter
: Accumulator
: Temporary accumulator
: Index register
: Extra pointer
: Stack pointer
: Program status
FFFD
H
Undefined
Undefined
Undefined
Undefined
Undefined
I-flag = 0, IL1, 0 = 11
Other bits are undefined.
Initial value
Structure of the Program Status Register
Vacancy
H
I
IL1, 0
N
Z
V
C
5
4
RP
PS
10
9
8
7
6
3
2
1
0
15
14
13
12
11
RP
CCR
Vacancy Vacancy