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8085

8085. Microcomputer. Major components of the computer - the processor, the control unit, one or more memory ICs, one or more I/O ICs, and the clock A single printed circuit board usually connects the ICs, making a computer called a microcomputer. Microcomputer. Basic Architecture.

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8085

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  1. 8085

  2. Microcomputer Major components of the computer - the processor, the control unit, one or more memory ICs, one or more I/O ICs, and the clock A single printed circuit board usually connects the ICs, making a computer called a microcomputer

  3. Microcomputer

  4. Basic Architecture • Princeton and Harvard • Princeton Architecture* • Known as Von Neumann architecture • Single memory contains both the program code and the data. • Harvard Architecture • Two separate memories. One contains only data while the other is containing only program code.

  5. Basic Architecture Princeton Harvard

  6. Major components Processor Control Unit Memory Clock

  7. Contents • Microprocessor Architecture

  8. Microprocessor ? A microprocessor is multi programmable clock driven register based semiconductor device that is used to fetch , process and execute a data within fraction of seconds.

  9. PIN CONFIGURATION

  10. THE 8085 AND ITS BUSSES • The 8085 is an 8-bit general purpose microprocessor that can address 64K Byte of memory. • It has 40 pins and uses +5V for power. It can run at a maximum frequency of 3 MHz. • -The pins on the chip can be grouped into 6 groups: • Address Bus. • Data Bus. • Control and Status Signals. • Power supply and frequency. • Externally Initiated Signals. • Serial I/O ports.

  11. The Address and Data Busses • The address bus has 8 signal lines A8 – A15 which are unidirectional. • The other 8 address bits are multiplexed (time shared) with the 8 data bits. • So, the bits AD0 – AD7 are bi-directional and serve as A0 – A7 and D0 – D7 at the same time. • During the execution of the instruction, these lines carry the address bits during the early part, then during the late parts of the execution, they carry the 8 data bits. • In order to separate the address from the data, we can use a latch to save the value before the function of the bits changes.

  12. 8085 ARCHITECTURE INTR INTA RST 5.5 RST 7.5 RST 6.5 SOD TRAP SID Interrupt controller Serial I/O controller 8 bit internal Data Bus Multiplexer Instruction Reg Temp Reg Accumulator Z temp W temp Reg array B C Flag Flip Flops D E Instruction Decoder and Machine Cycle Encoding H L Stack Pointer (16) ALU Program counter (16) Inc/dec latch Timing and control X1 Clk gen Data/ Address Buffer Address Buffer X2 Control Status DMA Reset S0 RD WR S1 ALE Clk out A15 –A8 Address Buss IO/M Reset out AD0 –AD7 Address/Data Buss HLDA HOLD Ready Reset in

  13. Flag Register The flags are affected by the arithmetic and logical instruction D7 D6 D5 D4 D3 D2 D1 D0 S Z AC P CY

  14. Accumulator • It is an 8 bit register • For any arithmetic and logical instruction one of the data should be in this register • It is used for storing the result of any arithmetic and logical manipulations. • It is also called as A register • All the data which are sent to I/O devices are sent via A register.

  15. Temporary register • It is used to hold the data during the operation of arithmetic and logical operation

  16. Sign Flag • If the D7 bit of the accumulator is set then this flag is set i.e 1 meaning that the result is in negative. • Ex. 7-8 = -1

  17. Carry flag • During the arithmetic operation if a carry occurs then this flag is set. • Ex. F1+1F= 10 1 Carry

  18. Zero flag • During the arithmetic/ logical operation if the result is zero then this flag is set. • Ex. FF-FF = 00

  19. Parity flag • After the of the arithmetic and logical operation if the result is even then this flag is set. • Ex. 0A-02 = 08

  20. Auxiliary carry flag • During BCD arithmetic operation when a carry is generated by D3 bit and passed on to D4 bit then this flag is set. • Ex. 1F+11 = 0000 1111 + 0001 0001 = 0010 0000

  21. Timing and control • It synchronizes all the operation with the clock and generates the communication between the microprocessor and peripherals

  22. Instruction Register and decoder • The instruction is loaded in the instruction register • The decoder decodes them and establishes the operation that has to be performed

  23. Register array • The W and Z register are temporary registers • Used to hold the 8 bit data during the execution and it is used internally . • It is not used by the programmer.

  24. Control and status signals

  25. Arithmetic and Logical unit • It is an 8 bit register • It is used for performing addition, subtraction and logical operation. • AND, OR, NOT, XOR, CMP are some of the logical operation.

  26. Program Counter • It is a 16 bit register • It is used to point out the address of the next instruction which is to be executed

  27. Stack pointer • It is a 16 bit register • It points the starting address of the stack .

  28. Register Array • B, C, D, E, H and L are general purpose register • All are 8 bit register • If the are combined as BC, DE and HL they can store 16 bit data

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