A microprocessor is an electronic component that is used by a computer to do its work. It is a central processing unit on a single integrated circuit chip containing millions of very small components including transistors, resistors, and diodes that work together. Some microprocessors in the 20th century required several chips. Microprocessors help to do everything from controlling elevators to searching the Web. Everything a computer does is described by instructions of computer programs, and microprocessors carry out these instructions many millions of times a second. [1] Microprocessors were invented in the 1970s for use in embedded systems. The majority are still used that way, in such things as mobile phones, cars, military weapons, and home appliances. Some microprocessors are microcontrollers, so small and inexpensive that they are used to control very simple products like flashlights and greeting cards that play music when you open them. A few especially powerful microprocessors are used in personal computers.

1. Program Flow Control
Instructions

2. Unconditional Jumps
• Unconditional Jumps
• The basic instruction that transfers control to another
point in the program is JMP. The basic syntax of JMP
instruction
General Form (Syntax):
• JMP label
• JMP is able to transfer control both forward and
backward.
• Here the CS and IP are unconditionally modified with
new CS and IP values.
• No flags are checked or affected by this instruction

3. Unconditional Jumps
• Intra-segment Jump or NEAR jump :
• If the target of JMP is in the same code segment,
it requires only the IP to be changed to transfer
control to the target location. This is called intra-
segment jump or NEAR jump
• Inter-segment or FAR jump :
• If the target for the instruction JMP is in different
code segment from that containing the JMP, then
IP and CS will be changed to transfer control to
the target location. Such a jump is called FAR or
Inter- Segment jump.

4. Unconditional Jumps
• Unlike JMP instruction that does an
unconditional jump, there are instructions
that do a conditional jumps (jump only when
some conditions are in act).
• The different types of conditional instruction
are as given in the next slide…

5. Jump instructions based on Flags
Instruction Description Condition Similar
Instructions
JC Jump if carry Carry = 1 JB, JNAE
JNC Jump if no carry Carry = 0 JNB, JAE
JZ Jump if zero Zero = 1 JE
JNZ Jump if not zero Zero = 0 JNE
JS Jump if sign Sign = 1 -
JNS Jump if no sign Sign = 0 -
JO Jump if overflow Ovrflw=1 -
JNO Jump if no Ovrflw Ovrflw=0 -
JP Jump if parity Parity = 1 JPE
JPE Jump if parity even Parity = 1 JP
JNP Jump if no parity Parity = 0 JPO
JPO Jump if parity odd Parity = 0 JNP

6. Jump Instructions based on Unsigned
numbers
Instruction Description Condition
Similar
Instructions
JA Jump if above (>) Carry=0, Zero=0 JNBE
JNBE Jump if not below or equal (not <=) Carry=0, Zero=0 JA
JAE Jump if above or equal (>=) Carry = 0 JNC, JNB
JNB Jump if not below (not <) Carry = 0 JNC, JAE
JB Jump if below (<) Carry = 1 JC, JNAE
JNAE Jump if not above or equal (not >=) Carry = 1 JC, JB
JBE Jump if below or equal (<=)
Carry = 1 or Zero
= 1
JNA
JNA Jump if not above (not >)
Carry = 1 or Zero
= 1
JBE
JE Jump if equal (=) Zero = 1 JZ
JNE Jump if not equal () Zero = 0 JNZ

7. Jump Instructions for signed numbers
Instruction Description Condition
Similar
Instructions
JG Jump if greater (>)
Sign = Ovrflw
or Zero=0
JNLE
JNLE
Jump if not less than or equal (not
<=)
Sign = Ovrflw
or Zero=0
JG
JGE Jump if greater than or equal (>=) Sign = Ovrflw JNL
JNL Jump if not less than (not <) Sign = Ovrflw JGE
JL Jump if less than (<) Sign Ovrflw JNGE
JNGE Jump if not greater or equal (not >=) Sign Ovrflw JL
JLE Jump if less than or equal (<=)
Sign Ovrflw or
Zero = 1
JNG
JNG Jump if not greater than (not >)
Sign Ovrflw or
Zero = 1
JLE
JE Jump if equal (=) Zero = 1 JZ
JNE Jump if not equal () Zero = 0 JNZ

8. Jump Instructions for signed numbers
Instruction Description Condition
Similar
Instructions
JG Jump if greater (>)
Sign = Ovrflw
or Zero=0
JNLE
JNLE
Jump if not less than or equal (not
<=)
Sign = Ovrflw
or Zero=0
JG
JGE Jump if greater than or equal (>=) Sign = Ovrflw JNL
JNL Jump if not less than (not <) Sign = Ovrflw JGE
JL Jump if less than (<) Sign Ovrflw JNGE
JNGE Jump if not greater or equal (not >=) Sign Ovrflw JL
JLE Jump if less than or equal (<=)
Sign Ovrflw or
Zero = 1
JNG
JNG Jump if not greater than (not >)
Sign Ovrflw or
Zero = 1
JLE
JE Jump if equal (=) Zero = 1 JZ
JNE Jump if not equal () Zero = 0 JNZ

9. Machine Control Instructions
• HLT : (Halt)
• This instruction causes the processor to enter to halt state.
• CPU stops fetching and executing instructions
• CPU is brought out of the halt state when reset signal is
given to it, or NMI is given or INTR pin goes high.
• NOP: (No Operation)
• This instruction is used to add wait states of 3 clock cycles.
• During these three clock cycles, CPU does not perform
anything.
• This instruction is useful in delay programs to add delay
loops

10. Machine Control Instructions
• WAIT
• This instruction causes the processor to enter into an idle state or a
wait state.
• Processor continues to remain in the wait state till a valid INTR or
NMI or a TEST pin goes high.
• It is used to synchronise with other external hardware such as Math
co-processor 8087.
• LOCK
• This instruction causes the processor to take control of the shared
resources.
• This is used as an instruction prefix to some critical instructions
which has to be executed.
• While LOCKED, it prevents the resources to be shared by other
processors.
• Example : LOCK IN AL,80H

11. Flag manipulation instructions
These instructions are used to change the status of flags in the
flag register such as Carry, Direction and Interrupt.
• CLC
• This instruction clears the Carry Flag
• CF  0
• CMC
• This instruction complements the Carry Flag
• CF  Complement of CF
• STC
• This instruction sets the Carry Flag
• CF  1

12. Flag manipulation instructions
• CLD
• This instruction clears the Direction Flag
• DF  0
• STD
• This instruction sets the Direction Flag
• DF  1
• CLI
• This instruction clears the Interrupt Flag
• IF  0
• STI
• This instruction sets the Interrupt Flag
• IF  1