R01UH0823EJ0100 Rev.1.00
Page 78 of 1823
Jul 31, 2019
RX23W Group
2. CPU
operation instruction, the bit decides whether the CPU will start handling the exception. When the bit is set to 0, the
exception handling is masked; when the bit is set to 1, the exception handling is enabled.
FV Flag (Invalid Operation Flag), FO Flag (Overflow Flag), FZ Flag (Division-by-Zero Flag),
FU Flag (Underflow Flag), and FX Flag (Inexact Flag)
While the exception handling enable bit (Ej) is 0 (exception handling is masked), if any of five floating-point exceptions
specified in the IEEE754 standard is generated, the corresponding bit is set to 1.
When Ej is 1 (exception handling is enabled), the value of the flag remains.
When the corresponding flag is set to 1, it remains 1 until it is cleared to 0 by software. (accumulation flag)
FS Flag (Floating-Point Error Summary Flag)
This bit reflects the logical OR of the FU, FZ, FO, and FV flags.
2.2.3
Accumulator
The accumulator (ACC0 or ACC1) is a 72-bit register used for DSP instructions. The accumulator is handled as a 96-bit
register for reading and writing. At this time, when bits 95 to 72 of the accumulator are read, the value where the value of
bit 71 is sign extended is read. Writing to bits 95 to 72 of the accumulator is ignored. ACC0 is also used for the multiply
and multiply-and-accumulate instructions; EMUL, EMULU, FMUL, MUL, and RMPA, in which case the prior value in
ACC0 is modified by execution of the instruction.
Use the MVTACGU, MVTACHI, and MVTACLO instructions for writing to the accumulator. The MVTACGU,
MVTACHI, and MVTACLO instructions write data to bits 95 to 64, the higher-order 32 bits (bits 63 to 32), and the
lower-order 32 bits (bits 31 to 0), respectively.
Use the MVFACGU, MVFACHI, MVFACMI, and MVFACLO instructions for reading data from the accumulator. The
MVFACGU, MVFACHI, MVFACMI, and MVFACLO instructions read data from the guard bits (bits 95 to 64), higher-
order 32 bits (bits 63 to 32), the middle 32 bits (bits 47 to 16), and the lower-order 32 bits (bits 31 to 0), respectively.
Note:
The value of bit 71 is sign extended for bits 95 to 72 and the extended value is always read. Writing to this area is
ignored.
b63
Value after reset: Undefined
b48 b47
b32 b31
b16 b15
b0
Range for reading by MVFACMI
b71
Range for reading and writing
by MVTACGU and MVFACGU
b64
b72
b95
ACC0
b63
b48 b47
b32 b31
b16 b15
b0
Range for reading and writing
by MVTACHI and MVFACHI
Range for reading and writing
by MVTACLO and MVFACLO
b71
b64
b72
b95
ACC1