D17133CS datasheet(106/289 Pages) NEC

106 / 289 page

CHAPTER 11

ARITHMETIC AND LOGIC UNIT

(3) CMP flag

When the CMP flag is set (1), the result of an arithmetic operation is not stored in either the general register

or data memory.

When the bit evaluation instruction is performed, the CMP flag is reset (0).

The CMP flag does not affect comparison evaluations, logical operations, or rotations.

(4) BCD flag

When the BCD flag is set (1), decimal correction is performed for all arithmetic operations. When the flag

is reset (0), decimal correction is not performed.

The BCD flag does not affect logical operations, bit evaluations, comparison evaluations, or rotations.

These flags can also be set through direct manipulation of the values in the program status word. When the flags

in the program status word are manipulated, the corresponding flag in the status flip-flop is also manipulated.

11.2.4 Performing Operations in 4-Bit Binary

When the BCD flag is set to 0, arithmetic operations are performed in 4-bit binary.

11.2.5 Performing Operations in BCD

When the BCD flag is set to 1, decimal correction is performed for arithmetic operations performed in 4-bit binary.

Table 11-2 shows the differences in the results of operations performed in 4-bit binary and in BCD. When the result

of an addition after decimal correction is equal to or greater than 20, or the result of a subtraction after decimal

correction is outside of the range –10 to +9, a value of 1010B (0AH) or higher is stored as the result (shaded area

in Table 11-2).

D17133CS Datasheet(PDF) 106 Page - NEC