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  • 1. Prof. Nitin Ahire 1 I/O Interfacing with 8085 Prof. Nitin Ahire XIE, Mahim
  • 2. Prof. Nitin Ahire 2 fundamentals of I/O devices • I/p Port I/P PORT BufferD0-D7 D0-D7 Enable Data from Keyboard
  • 3. Prof. Nitin Ahire 3 fundamentals of I/O devices • O/p Port O/P PORT latchD0-D7 D0-D7 Enable Data to Display
  • 4. Prof. Nitin Ahire 4 I/O interfacing techniques • Up support I/O interface tech. • It partitions memory from I/O, via software instruction like IN add, OUT add • When these instructions decoded by the processor it generate appropriate control signals IO/M^ • In 8085 it is possible to connect 256 I/O ports and 64Kb memory
  • 5. Prof. Nitin Ahire 5 I/O interfacing techniques • I/O devices can be interfaced in two ways 1) I/O mapped I/O 2) Memory mapped I/O
  • 6. Prof. Nitin Ahire 6 I/O interfacing techniques • Memory mapped I/O 1) In this device add is 16 bit ( A0-A15) 2) MEMR^ and MEWR^ control signals are used 3) Instructions are LDA add, STA Add, MOV A,M 4) Data trans. Bet reg and I/O devices 5) No. of I/O devices interface= 65536 ( Theoretically) • I/O mapped I/P 1) In this device add is 8 bit (A0-A7) 2) IOR^ and IOW^ control signals are used 3) Instruction are IN Add, OUT Add 4) Data trans. Bet acc and I/O devices 5) No. of I/O devices interface= 256 only
  • 7. Prof. Nitin Ahire 7 I/O device selection for add (80h) Decoder A0 A3 A2 A1 A6 A5 A4 A7 G1^ G2^ G Y0 OR RD^/ WR^ IO/M^ Buffer Or latch OR NOT OR To I/O device Data bus Enable IOR^/IOW^ Data bus
  • 8. Prof. Nitin Ahire 8 • IN 80h ( here 80h is the address of i/p switches) 8 0 A15/A7 A14/A6 A9/A1A10/A2A11/A3A12/A4A13/A5 A8/A0 1 0 00000 0
  • 9. Prof. Nitin Ahire 9 I/O device selection for add (80h) 3:8 Decoder A0 A3 A2 A1 A6 A5 A4 A7 G1^ G2^ G Y0 OR RD^/ WR^ IO/M^ Buffer Or latch OR NOT OR Data transfer to Accumulator EnableIOR^/IOW^ I/P switches S0-S7 Select lines Data bus
  • 10. Prof. Nitin Ahire 10 I/O device selection for add (81h) 3:8 Decoder A0 A3 A2 A1 A6 A5 A4 A7 G1^ G2^ G Y1 OR RD^/ WR^ IO/M^ Buffer Or latch OR NOT OR Data transfer to Accumulator EnableIOR^/IOW^ 0/P Display devices Select lines Data bus