HCS12 datasheet(307/452 Pages) FREESCALE

307 / 452 page

Glossary

S12CPUV2 Reference Manual, Rev. 4.0

Freescale Semiconductor

307

Operation:

Do until B = 0, leave SOP in Y : D, SOW in X

Partial Product = (M pointed to by X)

× (M pointed to by Y)

Sum-of-Products (24-bit SOP) = Previous SOP + Partial Product

Sum-of-Weights (16-bit SOW) = Previous SOW + (M pointed to by Y)

(X) + $0001

⇒ X; (Y) + $0001 ⇒ Y

(B) – $01

⇒ B

Description:

Performs weighted average calculations on values stored in memory. Uses

indexed (X) addressing mode to reference one source operand list, and

indexed (Y) addressing mode to reference a second source operand list.

Accumulator B is used as a counter to control the number of elements to be

included in the weighted average.

For each pair of data points, a 24-bit sum of products (SOP) and a 16-bit

sum of weights (SOW) is accumulated in temporary registers. When B

reaches zero (no more data pairs), the SOP is placed in Y : D. The SOW is

placed in X. To arrive at the final weighted average, divide the content of Y

: D by X by executing an EDIV after the WAV.

This instruction can be interrupted. If an interrupt occurs during WAV

execution, the intermediate results (six bytes) are stacked in the order

SOW[15:0], SOP[15:0], $00:SOP[23:16] before the interrupt is processed. The

wavr pseudo-instruction is used to resume execution after an interrupt. The

mechanism is re-entrant. New WAV instructions can be started and

interrupted while a previous WAV instruction is interrupted.

This instruction is often used in fuzzy logic rule evaluation. Refer to Section

9. Fuzzy Logic Support for more information.

WAV

Weighted Average

WAV

CCR Details:

HIN

––

–

Z: 1; set

H, N, V and C may be altered by this instruction

Source Form

Address

Mode

Object Code

Access Detail(1)

HCS12

M68HC12

WAV

Special

18 3C

Of(frr,ffff)O

Off(frr,fffff)O

(replace comma if interrupted)

SSS + UUUrr

SSSf + UUUrr

1. The replace comma sequence in parentheses represents the loop for one iteration of SOP and SOW accumulation.

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