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4-3

EIT

32182 Group User’s Manual (Rev.1.0)

4.2 EIT Events

4.2.1 Exception

(1) Reserved Instruction Exception (RIE)

Reserved Instruction Exception (RIE) occurs when execution of a reserved instruction (unimplemented

instruction) is detected.

(2) Address Exception (AE)

Address Exception (AE) occurs when an attempt is made to access a misaligned address in Load or Store

instructions.

(3) Floating-point Exception (FPE)

Floating-point Exception (FPE) occurs when Unimplemented Exception (UIPL) or one of the five exceptions

specified in the IEEE 754 standard (OVF/UDF/IXCT/DIV0/IVLD) is detected. Each exception processing is

outlined below.

1) Overflow Exception (OVF)

The exception occurs when the absolute value of the operation result exceeds the largest describable

precision in the floating-point format. The following table shows the operation results when an OVF oc-

curs.

Table 4.2.1 Operation Results When an OVF Occurred

Note 1: When the overflow exception enable (EO) bit (FPSR register bit 20) = "0"

Note 2: When the overflow exception enable (EO) bit (FPSR register bit 20) = "1"

Note: • If an OVF occurs while EIT processing for OVF is masked, an IXCT occurs at the same time.

• +MAX = H’7F7F FFFF, –MAX = H’FF7F FFFF

2) Underflow Exception (UDF)

The exception occurs when the absolute value of the operation result is less than the largest describable

precision in the floating-point format. The following table shows the operation results when a UDF occurs.

Table 4.2.2 Operation Results when a UDF Occurred

Note 1: When the underflow exception enable (EU) bit (FPSR register bit 18) = "0"

Note 2: When the underflow exception enable (EU) bit (FPSR register bit 18) = "1"

Sign of the Result

-Infinity

+Infinity

Rounding Mode

Nearest

Operation Result (Content

When the OVF EIT processing is

masked (Note 1)

+MAX

-Infinity

+Infinity

-MAX

+MAX

-MAX

+Infinity

-Infinity

of the Destination Register)

When the OVF EIT processing is

executed (Note 2)

No change

Operation Result (Content

When UDF EIT processing is masked (Note 1)

DN = 0: An unimplemented exception occurs

DN = 1: 0 is returned

of the Destination Register)

When UDF EIT processing is executed (Note 2)

No change

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