D17133CS datasheet(111/289 Pages) NEC

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CHAPTER 11

ARITHMETIC AND LOGIC UNIT

11.3.4 Addition and Subtraction When CMP=1 and BCD=1

BCD operations are performed.

The result is not stored in either the general register or data memory.

In other words, the operations specified by CMP=1 and BCD=1 are both performed at the same time.

Example

MOV

RPL, #0001B

; Sets the BCD flag (BCD=1).

MOV

PSW, #1010B

; Sets the CMP and Z flag (CMP=1, Z=1) and resets the CY flag

; (CY=0).

SUB

M1, #0001B

; <1>

SUBC

M2, #0010B

; <2>

SUBC

M3, #0011B

; <3>

By executing the instructions in steps numbered <1>, <2>, and <3>, the twelve bits in memory

locations M1, M2, and M3 and the immediate data (321) can be compared in decimal.

11.3.5 Cautions on Use of Arithmetic Operations

When performing arithmetic operations with the program status word (PSWORD), caution should be taken with

regard to the result of the operation being stored in the program status word.

Normally, the CY and Z flags in the program status word are set (1) or reset (0) according to the result of the

arithmetic operation being executed. However, when an arithmetic operation is performed on the program status

word itself, the result is stored in the program status word. This means that there is no way to determine if there

is a carry or borrow in the result of the operation nor if the result of the operation is zero.

However, when the CMP flag is set (1), results of arithmetic operations are not stored. Therefore, even in the

above case, the CY and Z flags will be properly set (1) or reset (0) according to the result of the operation.

11.4 LOGICAL OPERATIONS

As shown in Table 11-4, logical operations consist of logical OR, logical AND, and logical XOR. Accordingly, the

logical operation instructions are OR, AND, and XOR.

The OR, AND, and XOR instructions can be performed on either the general register and data memory, or on data

memory and immediate data. The operands of these instructions are specified in the same way as for arithmetic

operations ("r, m" or "m, #n4").

Logical operations are not affected by the BCD or CMP flags in the program status word (PSWORD). Logical

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

the index enable flag (IXE) is set (1), index modification is performed using the index register.

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