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CHAPTER 3 REGISTERS
3.3 Accumulator (A) and Temporary Accumulator (T)
The accumulator (A) and temporary accumulator (T) are application-specific registers
existing in the CPU.
The accumulator (A) is used as the area where the results of operations are temporarily
stored.
The temporary accumulator (T) is used as the area where the old data is temporarily
saved for data transfer to the accumulator (A) or the operand for operations.
■ Accumulator (A)
For 16-bit operation all 16 bits are used as shown in Figure 3.3-1. For 8-bit operation only the lower 8 bits
are used as shown in Figure 3.3-2.
Figure 3.3-1 Accumulator (A) Operation (16-bit Operation)
Figure 3.3-2 Accumulator (A) Operation (8-bit Operation)
■ Temporary Accumulator (T)
When 16-bit data is transferred to the accumulator (A), all the old 16-bit data in the accumulator is
transferred to the temporary accumulator (T) as shown in Figure 3.3-3. When 8-bit data is transferred to the
accumulator, old 8-bit data stored in the lower 8 bits of the accumulator is transferred to the lower 8 bits of
the temporary accumulator as shown in Figure 3.3-4. Although all 16-bits are used as the operand for 16-bit
operations as shown in Figure 3.3-5, only the lower 8 bits are used for 8-bit operations as shown in Figure
3.3-6.
ADDCW A
CF 1 CF 0
1234
H
5678
H
68AD
H
5678
H
Before execution After execution
AA
TT
ADDC A
CF CF
Before execution
After execution
1234
H
5678H
5678H
12ADH
1
0
A
T
T
A