KSI-W002-000

8

6.5

Arithmetic and Logic Unit (ALU)

This unit is used to perform arithmetic and logical operations such as addition,

comparison, and bit manipulation.

6.6

Carry Flag (CY)

The carry flag contains the carry generated by the arithmetic and logical unit immediately

after an operation. The set carry (SETB CY) and clear carry (CLRB CY) instructions allow

direct access for setting and clearing this flag.

6.7

Skip Flag (SF)

The skip flag is a 1-bit register, which enables programs to conditionally skip an instruction.

All instructions are executed when this flag is

, the program executes

NOP instruction and resets SF to “0”. Then program execution proceeds.

The following instructions affect the skip flag

Instructions

Set conditions of SF

Arithmetic

ADD n

INC L

If carry occurs

(L) = 0

Compare

IF0 @HL.b

IF0 CY

IFEQU @HL

IFEQU n

M[HL].b = 0

(CY) = 0

(A) = M[HL].b

(A) = n

Data Transfer

STA @HL+

XCH @HL+

(L) = 0

(L) = 0

The instructions, which doesn t affect the skip flag but have a skip condition, are as follows.

Instructions

Skip conditions

Data

Transfer

LDA n

LDL n

If it is continuous, skip next same

instruction.

If it is continuous, skip next same

instruction.

Bit

Manipulate

SETB H

CLRB H

If SETB H or CLRB H are continuous,

skip next

SETB H or CLRB H instruction.

SD6830