MA015 Datasheet, PDF (8/29 Pages) Megawin Technology Co., Ltd – Build-in watchdog timer

MA015 Datasheet
Version 2.00
5 Function Description
5.1 Registers
A
Y
X
P
PCH
PCL
1
S
5.2 Accumulator
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 two data words used in these operations.
5.3 Index Register(X,Y)
There are two 8-bit index registers (X and Y), which may be used to count program steps or to provide an 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-index of index address is possible.
5.4 Processor Status Register
The 8-bit processor status register contains seven status flags. Some of the flags are controlled by the program,
others may be controlled both the program and the CPU.
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
N
V
1
B
D
I
Z
C
N: Signed flag, 1 = negative, 0 = positive
V: Overflow flag, 1 = true, 0 = false
B: BRK interrupt command, 1 = BRK, 0 = IRQB
D: Decimal mode, 1 = true, 0 = false
I: IRQB disable flag, 1 = disable, 0 = enable
Z: Zero flag, 1 = true, 0 = false
C: Carry flag, 1 = true, 0 = false
5.5 Program Counter(PC)
The 16-bit program counter register provides the addresses, which step the micro-controller through sequential
program instructions. Each time the micro-controller fetch an instruction from program memory, the lower byte of
the program counter (PCL) is placed on the low-order 8 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.
5.6 Stack Point(S)
The stack pointer is an 8-bit register, which is used to control the addressing of the variable-length stack. The stack
pointer is automatically incremented and decremented under control of the micro-controller to perform stack
manipulations under direction of either the program or interrupts (/NMI or /IRQ). The stack allows simple
implementation of nested subroutines and multiple level interrupts. The stack pointer is initialized by the user’s
firmware.
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