a quick and easy note on microprocessor.

1. 8085 Microprocessor

2. Architectural Differences between
SAP1 And SAP2
• 16 bit program Counter(16-bit address bus )
• Loadable Program Counter(JMP instruction)
• 2-input port , 2-output port
• 64k Memory
• Memory Data Register(MDR)
• Temp, B, and C registers
• Arithmetic and Logical Operations
• Flags (Zero Flag and Sign Flag)
• 8-bit Opcode,42 Instruction
• Bidirectional Registers

3. Instructions
Memory Reference Instruction :LDA , STA, MVI
Register Instruction:MOV, ADD, SUB, INR, DCR
Logical Instruction:ORA/ORI, ANA/ANI, XRA/XRI,
CMA
Jump and Return :JMP/JZ/JNZ/JM and CALL/RET
Others: IN, OUT, HLT, NOP, RAR, RAR

4. Other Topics
• Flags
• T-State
• Conditional Jumps

5. Instruction affecting flag
Arithmetic and logical instructions:
(ADD,SUB,INR,DCR, ANA/ANI,ORA/ORI, XRA/XRI)

6. What you should know!!!
• Architecture
• Instructions
• Basic Programming
(Refer your books for several programming
examples )

7. Bonus Question
WALP to divide 41H by 10H.
(Hint: Repetitive subtraction. You may need use
Sign flag.)

8. 8085
8085
Architecture

10. ALU
Both Arithmetic and Logical Operation:
Operation Performed
Addition, Subtraction, Increment, Decrement
, Logical AND, Logical OR, Logical XOR, Compare
,Complement, Left/ Right Shift

11. Flags
Five Flags Available in 8085
Zero Flag(Z), Carry Flag(C), Auxiliary Carry(A),
Sign Flag(S), Parity Flag (P)

12. Timing and Control Signals
• The timing and control unit synchronizes all
the microprocessor operations with the clock
and generates the control signals necessary
for communication between the
microprocessor and peripherals.

13. INSTRUCTION REGISTER & DECODER:
• When an instruction is fetched from memory
it is placed in instruction register. Then it is
decoded and encoded into various machine
cycles.

14. REGISTER ARRAY:
• Apart from Accumulator (A-register), there are
six general-purpose programmable registers
• B, C, D, E, H and L.
• They can be used as 8-bit registers or paired to
store l6-bit data. The allowed pairs are B-C,D-E
and H-L.
• The temporary registers W and Z are intended
for internal use of the processor and it cannot be
used by the programmer.

15. Register Array:
STACK POINTER (SP):
• The stack pointer SP, holds the address of the
top of the stack.
• The stack is used to save the content of
registers during the execution of a program.

16. Register Array:
PROGRAM COUNTER (PC):
The program counter (PC) keeps track of program
execution. To execute a program the starting
address of the program is loaded in program
counter. The PC sends out an address to fetch a
byte of instruction from memory and increment its
content automatically. Hence, when a byte of
instruction is fetched, the PC holds the address of
the next byte of the instruction or next instruction.

17. Address Bus
• Consists of 16 address lines: A0 – A15
• Operates in unidirectional mode: The address
bits are always sent from the MPU to
peripheral devices, not reverse.
• 16 address lines are capable of addressing a
total of 216 = 65,536 (64k) memory locations.
• Address locations: 0000 (hex) – FFFF (hex)

18. Data Bus
• Consists of 8 data lines: D0 – D7
• Operates in bidirectional mode: The data bits
are sent from the MPU to peripheral devices,
as well as from the peripheral devices to the
microprocessor.
• Data range: 00 (hex) – FF (hex)