TS68040 datasheet(32/49 Pages) ATMEL

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TS68040

2116A–HIREL–09/02

Data Types and

Addressing Modes

The TS68040 supports the basic data types shown in Table 18. Some data types apply

only to the integer unit, some only to the FPU, and some to both the integer unit and the

FPU. In addition, the instruction set supports operations on other data types such as

memory addresses.

Note:

1. IU = Integer Unit.

The three integer data formats that are common to both the integer unit and the FPU

(byte, word, and long word) are the standard twos-complement data formats defined in

the TS68000 Family architecture. Whenever an integer is used in a floating-point opera-

tion, the integer is automatically converted by the FPU to an extended-precision floating-

point number before being used. The ability to effectively use integers in floating-point

operations saves user memory because an integer representation of a number usually

requires fewer bits than the equivalent floating-point representation.

Single- and double-precision floating-point data formats are implemented in the FPU as

defined by the IEEE standard. These data formats are the main floating-point formats

and should be used for most calculations involving real numbers.

The extended-precision data format is also in conformance with the IEEE standard, but

the standard does not specify this format to the bit level as it does for single- and dou-

ble-precision. The memory format for the FPU consists of 96 bits (three long words).

Only 80 bits are actually used; the other 16 bits are reserved for future use and for long-

word alignment of the floating-point data structures in memory. The extended-precision

format has a 15-bit exponent, a 64-bit mantissa, and a 1-bit mantissa sign. Extended-

precision numbers are intended for use as temporary variables, intermediate values, or

where extra precision is needed.

The TS68040 addressing modes are shown in Table 19. The register indirect address-

ing modes support post-increment, predecrement, offset, and indexing, which are

particularly useful for handling data structures common to sophisticated applications

and high-level languages. The program counter indirect mode also has indexing and off-

set capabilities; this addressing mode is typically required to support position-

independent software. In addition to these addressing modes, the TS68040 provides

index sizing and scaling features that enhance software performance. Data formats are

supported orthogonally by all arithmetic operations and by all appropriate addressing

modes.

Table 18. Data Types

Operand Data Type

Size

Execution Unit (IU

(1), FPU)

Notes

Bit

1-bit

Bit Field

1-32 bits

Field of consecutive bits

BCD

32 bits

Packaged: 2 digits byte

Unpacked: 1 digit byte

Byte Integer

8 bits

IU, FPU

Word Integer

16 bits

IU, FPU

Long-word Integer

32 bits

IU, FPU

Quad-word Integer

64 bits

Any two data registers

16-byte

128 bits

Memory-only, aligned 16-byte boundary

Single-precision Real

32 bits

FPU

1-bit sign, 8-bit exponent, 23-bit mantissa

Double-precision Real

64 bits

FPU

1-bit sign, 11-bit exponent, 52-bit mantissa

Extended-precision Real

80 bits

FPU

1-bit sign, 15-bit exponent, 64-bit mantissa

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