st2024c Sitronix Technology Corporation, st2024c Datasheet - Page 6

• Manufacturer Part Number: st2024c
• Description: 24k 8-bit Single Chip Microcontroller
• Manufacturer: Sitronix Technology Corporation

7
7.1
The accumulator is a general purpose 8-bit register which
stores the results of most arithmetic and logic operations. In
addition, the accumulator usually contains one of the two
data words used in these operations.
7.2
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.
7.3
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 incremented and decrement under
control
Ver 2.2
7
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C
C
P
P
Accumulator (A)
Index Registers (X,Y)
Stack Pointer (S)
of
U
U
the
PCH
microprocessor
1 0 0
8 7
7
7
7
7
6 5
to
CPU REGISTER MODEL
PCL
perform
A
Y
X
S
stack
0
0
0
0
0
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Accumulator A
Index Register Y
Index Register X
Program Counter PC
Stack Pointer S
manipulations under 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.
7.4
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
incremented each time an instruction or data is fetched from
program memory.
7.5
The 8-bit Processor Status Register contains seven status
flags. Some of the flags are controlled by the program,
others may be controlled both by the program and the CPU.
The instruction set contains a member of conditional branch
instructions which are designed to allow testing of these
flags.
Program Counter (PC)
Status Register (P)
ST2024C
1/31/08