21-03-2011, 12:11 PM
8085.ppt (Size: 256 KB / Downloads: 160)
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.