Accumulator (A) - Fujitsu F2MC-16LX Hardware Manual

2.4.1

Accumulator (A)

The accumulator (A) consists of the two 16-bit arithmetic operation registers AH and
AL. It is used as temporary storage for arithmetic operation results or for data
transfer. When AH and AL are used for 32-bit data processing, they are connected.
Only AL is used for word processing of 16-bit data or byte processing of 8-bit data.
■ Accumulator (A)
Data in the accumulator (A) can be used for arithmetic operations with data in the memory and
registers (Ri, RWi, and RLi). As with the F
that is not longer than a single word, the data in AL before the transfer is automatically
transferred to the AH (data retention function). In other words, processing efficiency can be
increased by using the data retention function and AL-AH arithmetic operations.
MOVL A,@RW1+6
A before execution
A after execution
MOVW A,@RW1+6
A before execution
A after execution
As shown in Figure 2.4-4, when data is transferred to the AL that is not longer than a byte, it is
expanded to 16 bits by signs or zeros and stored in AL. The data in the AL can also be handled
both as word or byte data. If an arithmetic operation instruction for byte processing is executed,
the higher eight bits of AL before the arithmetic operations are ignored. All higher eight bits of
the arithmetic operation result are set to "0".
Figure 2.4-2 Example of 32-bit Data Transfer
(This instruction reads long-word data at the address obtained by adding
the contents of RW1 to the 8-bit offset, and stores the read contents in A.)
XXXX XXXX
H H
DTB A6
H
2B52
8F74
H H
AH AL
Figure 2.4-3 Example of AL-AH Transfer
(This instruction reads word data at the address obtained by adding
the contents of RW1 to the 8-bit offset and stores the read contents in A.)
XXXX 1234
H H
DTB A6
H
1234 2B52
H H
AH AL
2 2
MC-8, when the F MC-16LX transfers data to the AL
MSB Memory space
A61540
8F
H H
A6153E 2B
H H
+6
RW1 15
H
MSB Memory space
A61540
8F
H H
A6153E 2B
H H
+6
RW1 15
H
2.4 Dedicated Registers
LSB
74
H
52
H
38
H
LSB
74
H
52
H
38
H
33