FUNCTION DESCRIPTION
Registers
A
Y
X
P
PCL
S
PCH
1
Accumulator
The accumulator is a 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.
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 MCU fetches the OP Code and the base
address, and modifies the address by adding the index register to the base address before
performing the desired operation. Pre- or post-index of index address is possible.
Processor Status Register (P)
The 8-bit processor status register contains seven status flags. Some flags are controlled by the
program,
Bit 7
N
and
others
Bit 6
V
may
Bit 5
1
be
controlled
Bit 4
B
by
both
the
program
and
Bit 1
Z
the
MCU.
Bit 0
C
Bit 3
D
Bit 2
I
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
Program Counter (PC)
The 16-bit program counter register provides the addresses, which steps MPC2F35 through the
sequential program instructions. Each time this MCU fetches 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 when an instruction or data is fetched from program memory.
MEGAWIN
MPC2F35_USB Data Sheet
5
MEGAWIN [ MEGAWIN TECHNOLOGY CO., LTD ]
