Motorola MC68340 manual Instruction Format and Notation, Instruction Word General Format

Freescale Semiconductor, Inc.

Freescale Semiconductor, Inc.

5.3.1.1.2Table Lookup and Interpolation (TBL). To maximize throughput for real-time applications, reference data is often precalculated and stored in memory for quick access. The storage of sufficient data points can require an inordinate amount of memory. The TBL instruction uses linear interpolation to recover intermediate values from a sample of data points, and thus conserves memory.

When the TBL instruction is executed, the CPU32 looks up two table entries bounding the desired result and performs a linear interpolation between them. Byte, word, and long- word operand sizes are supported. The result can be rounded according to a round-to- nearest algorithm or returned unrounded along with the fractional portion of the calculated result (byte and word results only). This extra precision can be used to reduce cumulative error in complex calculations. See 5.3.4 Using the TBL Instructions for examples.

5.3.1.2UNIMPLEMENTED INSTRUCTIONS. The ability to trap on unimplemented instructions allows user-supplied code to emulate unimplemented capabilities or to define special-purpose functions. However, Motorola reserves the right to use all currently unimplemented instruction operation codes for future M68000 enhancements. See 5.5.2.8 Illegal or Unimplemented Instructions for more details.

5.3.2Instruction Format and Notation

All instructions consist of at least one word. Some instructions can have as many as seven words, as shown in Figure 5-6. The first word of the instruction, called the operation word, specifies instruction length and the operation to be performed. The remaining words, called extension words, further specify the instruction and operands. These words may be immediate operands, extensions to the effective address mode specified in the operation word, branch displacements, bit number, special register specifications, trap operands, or argument counts.

15 0

OPERATION WORD

(ONE WORD, SPECIFIES OPERATION AND MODES)

SPECIAL OPERAND SPECIFIERS

(IF ANY, ONE OR TWO WORDS)

IMMEDIATE OPERAND OR SOURCE ADDRESS

EXTENSION

(IF ANY, ONE TO THREE WORDS)

DESTINATION EFFECTIVE ADDRESS EXTENSION

(IF ANY, ONE TO THREE WORDS)

Figure 5-6. Instruction Word General Format

5- 12MC68340 USER’S MANUALMOTOROLA

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