D17133CS datasheet(78/289 Pages) NEC

78 / 289 page

CHAPTER 7

SYSTEM REGISTER (SYSREG)

7.7.3 Index Enable Flag (IXE)

The IXE flag is used to enable to modify index of the data memory address, whether index modification is to be

performed on the data memory address used.

For a more detailed explanation, refer to 7.5 INDEX REGISTER (IX) AND DATA MEMORY ROW ADDRESS

POINTER (MEMORY POINTER: MP).

7.7.4 Zero Flag (Z) and Compare Flag (CMP)

The Z flag indicates whether the result of an arithmetic operation is 0. The CMP flag is used to specify that the

result of an arithmetic operation not be stored in data memory or the general register.

Table 7-2 shows how the CMP flag affects the setting and resetting of the Z flag.

Table 7-2. Zero Flag (Z) and Compare Flag (CMP)

Condition

When CMP=0

When CMP=1

When the result of the arithmatical operation is 0

← 1

Z remains unchanged

When the result of the arithmetic operation is other than 0 Z

← 0Z ← 0

The Z and CMP flags are used to compare the contents of the general register with those of the data memory.

The Z flag does not change other than in arithmetic operations; the CMP flag does not change other than in bit

decisions.

Example of 12-bit data comparision

;

Is the 12-bit data stored in M001, M002, and M003 equivalent to 456H?

CMP456:

SET2

CMP, Z

SUB

M001, #4

; Data stored in M001, M002, and M003 are not

SUB

M002, #5

; damaged

SUB

M003, #6

;

; CLR1

CMP

SKT

; CMP is automatically cleared by the bit decision instruction

DIFFER

;

≠ 456H

AGREE

; =456H

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