Motorola MCF5282, MCF5281 Introduction to the MAC, Multiply-Accumulate Functionality Diagram

Models: MCF5282 MCF5281

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Introduction to the MAC

A 48-bit accumulation data path to allow the use of a 40-bit product plus the addition of 8 extension bits to increase the dynamic number range when implementing signal processing algorithms.

The three areas of functionality are addressed in detail in following sections. The logic required to support this functionality is contained in a MAC module, as shown in Figure 3-1.

Operand Y

Operand X

X

Shift 0,1,-1

+/-

Accumulator(s)

Figure 3-1. Multiply-Accumulate Functionality Diagram

3.2Introduction to the MAC

The MAC is an extension of the basic multiplier found in most microprocessors. It is typically implemented in hardware within an architecture and supports rapid execution of signal processing algorithms in fewer cycles than comparable non-MAC architectures. For example, small digital filters can tolerate some variance in an algorithm’s execution time, but larger, more complicated algorithms such as orthogonal transforms may have more demanding speed requirements beyond the scope of any processor architecture and may require full DSP implementation.

To strike a balance between speed, size, and functionality, the ColdFire MAC is optimized for a small set of operations that involve multiplication and cumulative additions. Specifically, the multiplier array is optimized for single-cycle pipelined operations with a possible accumulation after product generation. This functionality is common in many signal processing applications. The ColdFire core architecture also has been modified to allow an operand to be fetched in parallel with a multiply, increasing overall performance for certain DSP operations.

Consider a typical filtering operation where the filter is defined as in Figure 3-2.

3-2

MCF5282 User’s Manual

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Motorola MCF5282, MCF5281 user manual Introduction to the MAC, Multiply-Accumulate Functionality Diagram