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INTEL 8085-Features
• INTEL 8085 is an 8-bit microprocessor.
• The data word size of the 8085 microprocessor is 8-bits. Hence has 8-bit data bus.
• The address size of 8085 microprocessor is 16-bits. Hence uses 16-bit address bus.
• It can directly process on 8-bits of data in single operation, hence it is known to be an 8-bit microprocessor.
• It can directly address 216 = 65,536 bytes i.e., 64 Kbytes (64 K memory locations) using 16-bits of address.
• 8085 microprocessor is fabricated using NMOS technology and comes in an 40-pin DIP(dual-in-line) package.
• It requires a single power supply of +5V.
• It has provision of internal frequency generation when an crystal is connected between the specified pins.
• The generated clock is divided by a factor of 2, hence to operate an 8085 based system at an frequency of 3 MHz, an crystal of 6 MHz frequency need to be connected to 8085.
• The NMOS 8085 is available in two versions 8085A and 8085A-2 with maximum internal clock frequency of 3.03 MHz and 5 MHz respectively and hence require an crystal of 6.06 MHz and 10 MHz to be connected them respectively.
• The enhanced version of 8085 is designed with HMOS transistors. It is available in three versions 8085AH, 8085AH-2, 8085AH-1 with maximum internal clock of 3 MHz, 5 MHz and 6 MHz respectively.
• The clock cycle of 8085 is of order of 320 ns and that for 8085AH-2 version is 200 ns.
• It has 80 basic instructions and 246 opcodes.
• 8085 is enhanced version of its predecessor the 8080A microprocessor; thus its instruction set is upward compatible with that of 8080A, i.e., 8085 instruction set includes all the 8080A instructions plus some more instructions.
• Thus the programs written for the 8080A will be executed by the 8085 microprocessor.
• But 8085 and 8080A are not pin compatible, i.e., the 8085 microprocessor can not be used in place of 8080A microprocessor in an 8080A based system.
INTEL 8085-Architecture
• The internal block diagram of 8085 microprocessor consists of the following main sections:
 An arithmetic and logic unit
 A timing and control unit
 A set of registers
ALU
• The arithmetic and logical unit(ALU), performs the following arithmetic and logical operations:
 Addition
 Subtraction
 Logical AND
 Logical OR
 Logical Exclusive-OR
 Complement (Logical NOT)
 Increment (add 1)
 Decrement(Subtract 1)
 Left shift, Right shift, Rotate Left,Rotate right
 Clear ………………e.t.c.
• Timing And Control Unit
• It is section of CPU.
• It generates timing and control signals which are necessary for the execution of instructions
• It controls data flow between CPU and peripherals (including memory).
• Provides status, control and timing signals which are required for the operation of memory and I/O devices.
• Controls all the operations of microprocessor and peripherals
Registers
• Registers are used by the microprocessor for temporary storage and manipulation of data and instructions.
• Data remains in the register till they are sent to the memory or I/O devices.
• INTEL 8085 microprocessor has the following registers:
 One 8-bit accumulator (ACC) i.e., Register-A
 Six 8-bit general purpose registers. These are B,C,D,E,H and L.
 One 16-bit stack pointer (SP)
 One 16-bit program counter (PC)
 Instruction register
 Temporary register
 Incrementer/Decrementer
 Flag register ( a register made up of individual flip-flops out of which only five are active.
• Accumulator:
 Accumulator is an 8-bit register associated with the ALU.
 It is used to hold one of the operands of an arithmetic or logical operation, the other operand is held in either one of the general purpose registers or in memory.
 After the operation is completed the accumulator holds the final result.