D17133CS datasheet(222/289 Pages) NEC

222 / 289 page

CHAPTER 18

INSTRUCTION SET

207

(3)

SUBC r, m

Subtract data memory from general register with carry flag

<1> OP code

00011

<2> Function

When CMP=0, (r)

← (r) – (m) – CY

Subtracts the data memory contents and the value of carry flag CY from the general register contents. Stores

the result in general register. By using this SUBC instruction, 2 or more words can be easily subtracted.

When CMP=1, (r) – (m) – CY

The result is not stored in the register. Carry flag CY and zero flag Z are changed, according to the result.

Sets carry flag CY, if a borrow occurs as a result of the subtraction. Resets the carry flag CY, if no borrow

occurs.

If the subtraction result is other than zero, zero flag Z is reset, regardless of compare flag CMP.

If the subtraction result is zero, with the compare flag reset (CMP=0), the zero flag Z is set.

If the subtraction result is zero, with the compare flag set (CMP=1), the zero flag Z is not changed.

Subtraction can be executed in binary 4-bit or BCD. The BCD flag for program status word PSWORD specifies

which kind of subtraction is to be executed.

<3> Example 1

Subtracts the 12-bit contents for addresses 0.2DH through 0.2FH from the 12-bit contents for addresses

0.0DH through 0.0FH and stores the result in 12 bits for addresses 0.0DH through 0.0FH, when row address

0 (0.00H-0.0FH) in bank 0 is specified as a general register:

(0.0FH)

← (0.0FH) – (0.2FH)

(0.0EH)

← (0.0EH) – (0.2EH) – CY

(0.0DH)

← (0.0DH) + (0.2DH) – CY

MEM00D

MEM

0.0DH

MEM00E

MEM

0.0EH

MEM00F

MEM

0.0FH

D17133CS Datasheet(PDF) 222 Page - NEC