eorex
MCU Description
Item
Accumulator
(Preliminary)
EU1010 / EU1011
Abbreviation
ACC
Description
The EU101x has an 8-bit register used for data hold,
exchange, arithmetic, transfer and I/O operation.
In EU101x that builds in two index registers ( X and Y ).
These two index registers could be used to count program
steps or to provide an index value to be used in generating as
effective address.
When executing an instruction which specifies indexed
addressing, the MCU fetches the operation code and the
base address, and modifies the address by adding the index
register to its prior to perform the desired operation. Per or
post-index of indirect address is possible.
The EU101x includes some special function control registers
in zero-page. For more detailed information about the special
function registers, please refer to next section.
The stack pointer is an 8-bit register that is used to control
the addressing of the variable-length stack. The stack pointer
is automatically incremented and decremented under control
of the microprocessor the perform stack manipulations under
direction of either the program or interrupts. The stack allows
a simple implementation of nested subroutines and multiple
level interrupts. The stack pointer is initialized by the user’s
software.
The 14-bit program counter register provides the address
that step the microprocessor through sequential program
instructions.
The 8-bit status flag register contains seven status flags.
Some of the flags are controlled by the program and others
may be controlled both by the program and the MCU.
Instruction set contains a number of conditional branch
instructions that are designed to allow testing of these flags.
Index Register
(X,Y)
Special Function
Register
SFR
Stack pointer
register
SP
Program counter
PC
Program Flag
Register
P
Aug.2007
3/21
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