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Instruction Glossary

S12CPUV2 Reference Manual, Rev. 4.0

258

Freescale Semiconductor

Operation:

MIN-MAX Rule Evaluation

Description:

Performs an unweighted evaluation of a list of rules, using fuzzy input values

to produce fuzzy outputs. REV can be interrupted, so it does not adversely

affect interrupt latency.

The REV instruction uses an 8-bit offset from a base address stored in index

REV to execute correctly, each rule in the knowledge base must consist of

a table of 8-bit antecedent offsets followed by a table of 8-bit consequent

offsets. The value $FE marks boundaries between antecedents and

consequents and between successive rules. The value $FF marks the end

of the rule list. REV can evaluate any number of rules with any number of

inputs and outputs.

Beginning with the address pointed to by the first rule antecedent, REV

evaluates each successive fuzzy input value until it encounters an $FE

separator. Operation is similar to that of a MINA instruction. The smallest

input value is the truth value of the rule. Then, beginning with the address

pointed to by the first rule consequent, the truth value is compared to each

successive fuzzy output value until another $FE separator is encountered;

if the truth value is greater than the current output value, it is written to the

output. Operation is similar to that of a MAXM instruction. Rules are

processed until an $FF terminator is encountered.

Before executing REV, perform these set up operations.

• X must point to the first 8-bit element in the rule list.

• Y must point to the base address for fuzzy inputs and fuzzy outputs.

• A must contain the value $FF, and the CCR V bit must = 0.

(LDAA #$FF places the correct value in A and clears V.)

• Clear fuzzy outputs to 0s.

Index register X points to the element in the rule list that is being evaluated.

X is automatically updated so that execution can resume correctly if the

instruction is interrupted. When execution is complete, X points to the next

address after the $FF separator at the end of the rule list.

REV

Fuzzy Logic Rule Evaluation

REV

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