st2064b Sitronix Technology Corporation, st2064b Datasheet - Page 6

• Manufacturer Part Number: st2064b
• Description: 8 Bit Microcontroller With 64k Bytes Rom
• Manufacturer: Sitronix Technology Corporation

7
Register Model
Accumulator (A)
The Accumulator is a general-purpose 8-bit register that stores
the results of most arithmetic and logic operations. In addition,
the accumulator usually contains one of the two data which
used in these operations.
Index Registers (X,Y)
There are two 8-bit Index Registers (X and Y), which may be
used to count program steps or to provide and index value to
be used in generating an effective address. When executing an
instruction, which specifies indexed addressing, the CPU
fetches the OP code and the base address, and modifies the
address by adding the index register to it prior to performing
the desired operation. Pre or post-indexing of indirect
addresses is possible.
Stack Pointer (S)
The Stack Pointer is an 8-bit register, which is used to control
the addressing of the variable-length stack. It’ s range from
100H to 1FFH total for 256 bytes (128 level deep). The stack
pointer is automatically increment and decrement under control
of the microprocessor to perform stack manipulations under
Ver. 3.0
7
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C
C
Bit 7
N
P
P
U
U
Bit 7:
1 = Negative
0 = Positive
Bit 6:
1 = Negative
0 = Positive
Bit 4:
1 = BRK interrupt occur
0 = Non BRK interrupt occur
PCH
N : Signed flag by arithmetic
V : Overflow of signed Arithmetic flag
B : BRK interrupt flag
Bit 6
V
1
7
7
7
7
7
Bit 5
1
PCL
A
Y
X
S
TABLE 7-1 Status Register (P)
Bit 4
0
0
0
0
0
B
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direction of either the program or interrupts (IRQ). The stack
allows simple implementation of nested subroutines and
multiple level interrupts. The stack pointer is initialized by the
user’ s software.
Program Counter (PC)
The 16-bit Program Counter register provides the address,
which step the microprocessor through sequential program
instructions. Each time the microprocessor fetches and
instruction from program memory, the lower byte of the
program counter (PCL) is placed on the low-order bits of the
address bus and the higher byte of the program counter (PCH)
is placed on the high-order 8 bits. The counter is increment
each time an instruction or data is fetched from program
memory.
Status Register (P)
The 8-bit Processor Status Register contains seven status flags.
Some of these flags are controlled by program; others may be
controlled both by the program and the CPU. The instruction
set contains a member of conditional branch instructions that
are designed to allow testing of these flags. Refer to TABLE 7-1
Accumulator A
Index Register Y
Index Register X
Program Counter PC
Stack Pointer S
Bit 3
D
Bit 3:
1 = Decimal mode
0 = Binary mode
Bit 2:
1 = Interrupt disable
0 = Interrupt enable
Bit 1:
1 = Zero
0 = Non zero
Bit 0:
1 = Carry
0 = Non carry
D : Decimal mode flag
I : Interrupt disable flag
Z : Zero flag
C : Carry flag
Bit 2
I
Bit 1
Z
ST2064B
Bit 0
C
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