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CHAPTER 3 REGISTERS
3.3.1 How To Use The Temporary Accumulator (T)
The F
2
MC-8FX CPU has a special-purpose register called a temporary accumulator. This
section described the operation of this register.
■ How to Use the Temporary Accumulator (T)
The F
2
MC-8FX CPU has various binary operation instructions, some data transfer instructions and the
temporary accumulator (T) for 16-bit data operation. Although there is no instruction for direct data
transfer to the temporary accumulator, the value of the original accumulator is transferred to the temporary
accumulator before executing the instruction for data transfer to the accumulator. Therefore, to perform
operations between the accumulator and temporary accumulator, execute operations after carrying out the
instruction for data transfer to the accumulator twice. Since data is not automatically transferred by all
instructions to the temporary accumulator, see the columns of TL and TH in the instruction list for details
of actual data transfer instructions. An example of addition with carry of 16-bit data stored at addresses
1280
H
and 0042
H
is shown below.
Figure 3.3-7 shows the operation for the accumulator and temporary accumulator when the above example
is executed.
Figure 3.3-7 Operation of Accumulator (A) and Temporary Accumulator (T) in Word Data Processing
MOVW A, 0042H -
MOVW A, 1280H -
ADDCW A -
A A A
T T T CF T
RAM RAM RAM RAM
78H 78H 78H 78H
56H 56H 56H 56H
34H 34H 34H 34H
12H 12H 12H 12H
XXXXH
XXXXH
XXXXH
1234H
5678H
1234H
68ACH
1234H
1281H
1280H
0043H
0042H
1281H
1280H
0043H
0042H
1281H
1280H
0043H
0042H
1281H
1280H
0043H
0042H
0
...
...
...
...
...
...
...
...
Before execution
Last result
+
A