HCS12 datasheet(364/452 Pages) FREESCALE

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S12CPUV2 Reference Manual, Rev. 4.0

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Freescale Semiconductor

9.6 WAV Instruction Details

The WAV instruction performs weighted average calculations used in

defuzzification. The pseudo-instruction wavr is used to resume an

interrupted weighted average operation. WAV calculates the numerator and

denominator sums using:

Where n is the number of labels of a system output, Si are the singleton

positions from the knowledge base, and Fi are fuzzy outputs from RAM. Si

and Fi are 8-bit values. The 8-bit B accumulator holds the iteration count n.

Internal temporary registers hold intermediate sums, 24 bits for the

numerator and 16 bits for the denominator. This makes this instruction

suitable for n values up to 255 although eight is a more typical value. The

final long division is performed with a separate EDIV instruction immediately

after the WAV instruction. The WAV instruction returns the numerator and

denominator sums in the correct registers for the EDIV. (EDIV performs the

unsigned division Y = Y : D / X; remainder in D.)

Execution time for this instruction depends on the number of iterations

(labels for the system output). WAV is interruptible so that worst case

interrupt latency is not affected by the execution time for the complete

weighted average operation. WAV includes initialization for the 24-bit and

16-bit partial sums so the first entry into WAV looks different than a resume

from interrupt operation. The CPU12 handles this difficulty with a

pseudo-instruction (wavr), which is specifically intended to resume an

interrupted weighted average calculation. Refer to 9.6.3 Cycle-by-Cycle

Details for WAV and wavr for more detail.

9.6.1 Set Up Prior to Executing WAV

Before executing the WAV instruction, index registers X and Y and

accumulator B must be set up. Index register X is a pointer to the Si

singleton list. X must have the address of the first singleton value in the

knowledge base. Index register Y is a pointer to the fuzzy outputs Fi. Y must

have the address of the first fuzzy output for this system output. B is the

iteration count n. The B accumulator must be set to the number of labels for

this system output.

System Output

∑

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