PLQP0048KB-B datasheet(37/177 Pages) RENESAS

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R01DS0261EJ0110 Rev.1.10

Page 37 of 177

Oct 30, 2015

RX230 Group, RX231 Group

2. CPU

(9)

Floating-point status word (FPSW)

The floating-point status word (FPSW) indicates the results of floating-point operations.

When an exception handling enable bit (Ej) enables the exception handling (Ej = 1), the exception cause can be identified

by checking the corresponding Cj flag in the exception handling routine. If the exception handling is masked (Ej = 0), the

occurrence of exception can be checked by reading the Fj flag at the end of a series of processing. Once the Fj flag has

been set to 1, this value is retained until it is cleared to 0 by software (j = X, U, Z, O, or V).

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.

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