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4
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
0
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