UPD17P136ACT datasheet(115/292 Pages) NEC

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CHAPTER 11 ARITHMETIC AND LOGIC UNIT (ALU)

11.6 COMPARISON JUDGEMENTS

As shown in Table 11-7, there are comparison judgement instructions for determining if one value is “equal to”,

“not equal to”, “greater than or equal to”, or “less than” another.

The SKE instruction is used to determine if two values are equal. The SKNE instruction is used to determine two

values are not equal. The SKGE instruction is used to determine if one value is greater than or equal to another and

the SKLT instruction is used to determine if one value is less than another.

The SKE, SKNE, SKGE, and SKLT instructions perform comparisons between a value in data memory and

immediate data. In order to compare values in the general register and data memory, a subtraction instruction is

performed according to the values in the CMP and Z flags in the program status word (PSWORD). For more

information concerning comparison of the general register and data memory, see 11.3 ARITHMETIC OPERATIONS.

Comparison judgements are not affected by the BCD or CMP flags in the program status word (PSWORD) and

comparison judgements do not cause either the CY or Z flags in the program status word (PSWORD) to be set.

11.6.1 to 11.6.4 explain the “equal to”, “not equal to”, “greater than or equal to”, and “less than” comparison

evaluations.

Table 11-7. Comparison Judgement Instructions

11.6.1 “Equal to” Judgement

The "equal to" judgement instruction (SKE m, #n4) is used to determine if immediate data and the contents of a

location in data memory are equal.

This instruction causes the next instruction to be skipped when the immediate data and the contents of data memory

are equal.

Example

MOV

M1,

#1010B

SKE

M1,

#1010B

; (1)

;

SKE

M1,

#1000B

; (2)

In this example, because the contents of data memory M1 and immediate data 1010B in step number

(1) are equal, the program branches to B. In step number (2), because the contents of data memory

M1 and immediate data 1000B are not equal, the program branches to C.

Equal to

SKE m, #n4

Not equal to

SKNE m, #n4

Greater than or equal to

SKGE m, #n4

Less than

SKLT m, #n4

Comparison

judgement

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