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Explain the $\overline{LOCK}$ & $\overline{TEST}$ Signal?

Mumbai University > Electronics and Telecommunication > Sem 4 > Microprocessor and peripherals

Marks: 5M

Year: May 2015

1 Answer
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$\overline{LOCK}$ :-

  1. n minimum mode this line carries the $\overline{WR}$ signal indicates a write operation when this pin is low.
  2. It is used with $M/ \overline{IO}$ to write to memory or IO device.
  3. In maximum mode it functions as the $\overline{LOCK}$output line.
  4. When 8086 executes an instruction with the LOCK prefix this signal is active (i.e. low) remains active till next instruction indicating the external bus master cannot take control of the system bus.

$\overline{TEST}$:-

  1. It is an active low input line dedicated for 8087 co-processor.
  2. In minimum mode it is connected to GND.
  3. In maximum mode whenever the co-processor is busy it makes this pin high.
  4. $\overline{TEST}$ input is examined by the WAIT instruction.
  5. If the $\overline{TEST}$pin is high, the microprocessor enters idle state till $\overline{TEST}$ pin becomes low i.e. 8087 is free.
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