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

CHAPTER 2 CPU
2.3.1

Accumulator (A)

The function of accumulator (A) is explained.
Accumulator (A)
The accumulator (A) consists of two 16-bit length arithmetic operation registers (AH/AL) to be used for the
temporary storage of operation result and data transfer, etc. The AH and the AL are concatenated to be used
for the 32 bit data process. Only the AL is used for the word process in the 16-bit data process mode or for
the byte process in the 8-bit data process mode. Data stored in the accumulator (A) can be used for
operations with data in the memory and registers (Ri, RWi, and Rli). In the same manner as the F
when a data item shorter than the word length is transferred to the AL, the data item in the AL before the
transfer is automatically transferred to the AH (data hold function). Improvement of the process efficiency
is supported by the data hold function and the operation between AL and AH.
When data shorter than the byte length is transferred to the AL, the data is sign-extended or zero-extended
to 16-bit length data items and stored in the AL. Data in the AL can be handled as those in word or byte
length.
When the arithmetic operation instruction of byte process is executed in the AL, the upper eight-bit of the
AL before operation are ignored and all the upper eight bits of the operation result become 0. The
accumulator (A) value is not initialized by the reset and is undefined value immediately after the reset.
Figure 2.3-3 shows the 32-bit data transfer process, and Figure 2.3-4 shows the AL-AH transfer process.
MOVW A,@RW1+6
A before
the execution
A after
the execution
MOVW A,@RW1+6
A before
the execution
A after
the execution
34
Figure 2.3-3 32-bit Data Transfer
XXXX
XXXX
H
H
A6
DTB
2B52
8F74
H
H
Figure 2.3-4 AL-AH Transfer
XXXX 1234
H H
DTB A6
1234 2B52
H H
MSB
A61540
H
A6153E
H
H
+6
RW1
MSB
A61540
H
A6153E
H
H
+6
RW1
8F 74
H H
2B
52
H
H
15 38
H H
LSB
8F 74
H H
2B 52
H H
38
15
H
H
2
MC-8L,
LSB