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TK2633. 8085 Microprocessor Architecture – Demultiplexing the AD7-AD0. DR MASRI AYOB. Bus Demultiplexer AD 7 -AD 0. It is necessary to have the knowledge and skills to demultiplex data bus and address bus as it is important in hardware design applications.

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tk2633

TK2633

8085 Microprocessor Architecture – Demultiplexing the AD7-AD0

DR MASRI AYOB

bus demultiplexer ad 7 ad 0
Bus Demultiplexer AD7-AD0
  • It is necessary to have the knowledge and skills to demultiplex data bus and address bus as it is important in hardware design applications.
  • Like previous example (referring to timing diagram): MOV C,A => with machine code (4FH)
bus demultiplexer ad 7 ad 02
Bus Demultiplexer AD7-AD0
  • From fig 1, to run instruction MOV C, A the high order address bus maintained as bus address for three clock periods.
  • However the low order address bus (05H) was eliminated after first time state.
  • The address need to be latched as to identify memory address.
  • After T1, the bus AD7-AD0 now becomes 4FH.
bus demultiplexer ad 7 ad 03
Bus Demultiplexer AD7-AD0
  • In Fig 2, the AD7-AD0 bus is connected to the input of latch buffer 74LS373.
  • The ALE signal is connected to enable pin (G) at latch, and the output control signal is grounded (OC).
  • When the ALE signal is active high, the latch will act according to the input instruction (the output changes according to input data).
  • At T1 the latch output value is 05H, and when ALE is low, the byte data 05H is hold until the new next ALE signal activated.
  • This causes the output latch is low order address memory A7-A0 (05H).
control signals
Control Signals
  • It is necessary to generate two RD control signals, one for memory and one for peripheral.
  • Similar to WR control signal; one for writing to memory and one for writing to output peripheral.
control signals1
Control Signals

Figure 3: Example of schematic diagram to generate control signals.

control signals and demultiplexing
Control Signals and Demultiplexing

Figure 4:the combination of control signals as well as demultiplexing the bus system.