UPD17P136ACT datasheet(113/292 Pages) NEC

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CHAPTER 11 ARITHMETIC AND LOGIC UNIT (ALU)

11.5 BIT JUDGEMENTS

As shown in Table 11-6, there are both TRUE (1) and FALSE (0) bit judgement instructions.

The TRUE (1) and FALSE (0) bit judgements use SKT and SKF instruction, respectively

The SKT and SKF instructions can only be used with data memory.

Bit judgements are not affected by the BCD flag in the program status word (PSWORD) and bit judgements do

not cause either the CY or Z flag in the program status word (PSWORD) to be set. However, when an SKT or SKF

instruction is executed, the CMP flag is reset (0). When the index enable flag (IXE) is set (1), index modification is

performed using the index register. For information concerning index modification using the index register, see

CHAPTER 7 SYSTEM REGISTER (SYSREG).

11.5.1 and 11.5.2 explain TRUE (1) and FALSE (0) bit judgements.

Table 11-6. Bit Judgement Instructions

11.5.1 TRUE (1) Bit Judgement

The TRUE (1) bit judgement instruction (SKT m, #n) is used to determine whether or not the bits specified by n

in the 4 bits of data memory m are TRUE (1). When all bits specified by n are TRUE (1), this instruction causes the

next instruction to be skipped.

Example

MOV

M1,

#1011B

SKT

M1,

#1011B

; (1)

SKT

M1,

#1101B

; (2)

In this example, bits 3, 1, and 0 of data memory M1 are judged in step number (1). Because all the

bits are TRUE (1), the program branches to B. In step number (2), bits 3, 2, and 0 of data memory

M1 are judged. Since bit 2 of data memory M1 is FALSE (0), the program branches to C.

TRUE (1) bit judgement

SKT m, #n

FALSE (0) bit judgement

SKF m, #n

Bit judgement

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