R01UH0823EJ0100 Rev.1.00
Page 90 of 1823
Jul 31, 2019
RX23W Group
2. CPU
2.7
Operation of Instructions
2.7.1
Restrictions on RMPA and String-Manipulation Instructions
2.7.1.1
Transfer Size and Data Prefetching
The RMPA instruction and the string-manipulation instructions (SCMPU, SMOVB, SMOVF, SMOVU, SSTR, SUNTIL,
and SWHILE instructions) transfer data in longword units to speed up the reading of data from and writing of data to the
memory. If the last of the data to be processed is less than a longword, data transfer proceeds with the sizes described
below:
RMPA, SSTR, SUNTIL, and SWHILE instructions: Size specified by the size specifier
SCMPU, SMOVB, SMOVF, and SMOVU instructions: Byte
Additionally, in the above processing, the RMPA instruction and the string-manipulation instructions other than the
SSTR instruction (that is, the SCMPU, SMOVB, SMOVF, SMOVU, SUNTIL, and SWHILE instructions) prefetch data
when reading data from the memory. Data is prefetched from the prefetching start position with three bytes as the upper
limit. The prefetching start positions of each operation are shown below.
RMPA instruction: The multiplicand address specified by R1, and the multiplier address specified by R2
SCMPU instruction: The source address specified by R1 for comparison, and the destination address specified by
R2 for comparison
SUNTIL and SWHILE instructions: The destination address specified by R1 for comparison
SMOVB, SMOVF, and SMOVU instructions: The source address specified by R2 for transfer
2.7.1.2
Access to the External Space
Although the external space has a per-area ending-switching facility (only for data), the allocation of data to be handled
by RMPA or string-manipulation instructions (SCMPU, SMOVB, SMOVF, SMOVU,SSTR, SUNTIL, and SWHILE
instructions) to an area where the endian differs from that of the chip is prohibited, and operation is not guaranteed if this
restriction is not observed. If data to be handled by RMPA or string-manipulation instructions are allocated to the
external space, they must be allocated to areas where the endian setting is the same as that for the chip.
2.7.1.3
Access to I/O Registers
The allocation of data to be handled by RMPA or string-manipulation instructions (SCMPU, SMOVB, SMOVF,
SMOVU, SSTR, SUNTIL, and SWHILE instructions) to I/O registers is prohibited, and operation is not guaranteed if
this restriction is not observed.