Mc68060 Fpu Data Formats And Data Types - Motorola M68060 User Manual

New AEXC Bit
6.1.4 Floating-Point Instruction Address Register (FPIAR)
For the subset of the floating-point instructions that generate exception traps, the FPU loads
the 32-bit FPIAR with the logical address of the instruction before executing the instruction.
Because the integer unit can execute instructions while the FPU executes floating-point
instructions, the program counter (PC) value stacked by the MC68060 in response to a float-
ing-point exception handler may not point to the offending instruction. Therefore, a floating-
point exception handler uses the address in the FPIAR to locate a floating-point instruction
that has caused an exception. Since the FMOVE to/from the FPCR, FPSR, or FPIAR and
FMOVEM instructions cannot generate floating-point exceptions, these instructions do not
modify the FPIAR. However, they can be used to read the FPIAR in an exception handler
without changing the previous value. A reset or a restore operation of the null state clears
the FPIAR.
6.2 FLOATING-POINT DATA FORMATS AND DATA TYPES
The M68000 floating-point model (MC68881, MC68882, MC68040, and MC68060) supports
the following floating-point data formats: single precision, double precision, extended
precision, and packed decimal. The M68000 floating-point model supports the following
data types: normalized, zeros, infinities, unnormalized numbers, denormalized numbers,
and NANs. The MC68060 supports part of the M68000 floating-point model in hardware.
Table 6-3 lists the floating-point data formats and data types supported by the MC68060.
Table 6-4 through Table 6-7 summarize the floating-point data formats and data types
details.
Table 6-3. MC68060 FPU Data Formats and Data Types
Single-
Number Types
Precision
Real
Normalized
Zero
Infinity
NAN
Denormalized
Unnormalized
*
Data Format/Type Supported by On-Chip MC68060 FPU Hardware
†
Data Format/Type Supported by Software (M68060SP)
MOTOROLA
= Old AEXC Bit
IOP = IOP
OVFL = OVFL
UNFL = UNFL
DZ = DZ
INEX = INEX
Double- Extended-
Precision Precision
Real
* *
* *
* *
* *
† †
— —
M68060 USER'S MANUAL
+ EXC Bits
+ (BSUN + SNAN + OPERR)
+ (OVFL)
+ (UNFL • INEX2)
+ (DZ)
+ (INEX1 + INEX2 + OVFL)
Data Formats
Packed-
Decimal
Integer
Real Real
* †
* †
* †
* †
† †
† †
Floating-Point Unit
Byte Word Long-Word
Integer Integer
* *
* *
— —
— —
— —
— —
*
*
—
—
—
—
6-7