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MB90420/5 (A) SERIES F
2.7.1 Accumulator (A)
An accumulator (A) consists of two 16-bit length operation registers (AH and AL) used for temporary storage
of the operation result or data.
The A register can be used as a 32-, 16-, or 8-bit register. Various operations can be performed between
the A register and memory or the other register, or between the AH register and the AL register. The A
register has a data-hold function; when data equal to or shorter than the word length is transferred to the AL
register, the AL register data before the transfer is transferred automatically to the AH register (This function
does not work depending on the instruction).
n Accumulator (A)
• Data transfer to accumulator
The accumulator can process 32-bit data (long word), 16-bit data (word), and 8-bit data (byte). There are
also 4-bit transfer instructions (MOVN), but they are explained here as 8-bit data.
– When processing 32-bit data, the AH register and the AL register are concatenated and used.
– When processing 16- or 8-bit data, only the AL register is used.
– When transferring data equal to or shorter than the byte length to the AL register, the data is sign-
extended or zero-extended to be the 16-bit length and stored in the AL register. Data in the AL register
can also be treated in word and byte lengths.
Figure 2.13 shows how data is transferred to the accumulator, and Figures 2.14 to 2.17 show concrete
transfer examples.
*: 000
2
MC-16LX FAMILY 16-BIT MICROCONTROLLERS HARDWARE MANUAL
32-bit Data transfer
16-bit Data transfer
8-bit Data transfer
or FFF
when 4-bit transfer instruction executed
H
H
Fig. 2.13 Data Transfer to Accumulator
32 bits
AH
Data transfer Data transfer
AH
Data save
AH
Data save
00
(zero-extended or sign-extended)
2-16
AL
AL
Data transfer
AL
*
or FF
Data transfer
H
H
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