To put the 8085 microprocessor in the wait state, one should:
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To put the 8085 microprocessor in the wait state, one should:
Answer: B. lower the READY input — ConceptThe 8085 uses the READY input to synchronize a machine cycle with memory or an I/O device that cannot respond at the processor normal speed. READY is…
- A.
lower the HOLD input
- B.
lower the READY input
- C.
raise the HOLD input
- D.
raise the READY input
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Show answer & explanation
Correct answer: B
Concept
The 8085 uses the READY input to synchronize a machine cycle with memory or an I/O device that cannot respond at the processor normal speed.
READY is sampled as an active-high readiness signal: a low level extends the current machine cycle, whereas HOLD/HOLDA transfers bus ownership for DMA and serves a different purpose.
Application
Suppose a slow memory device cannot complete a read cycle within the normal 8085 timing and therefore keeps READY low.
When the processor samples this low level near the end of T2, it inserts one or more TW states between T2 and T3 instead of completing the cycle.
Once the device raises READY, the processor leaves the wait sequence and continues to T3, allowing the bus cycle to finish.
Cross-check and contrast
The control-line meanings separate the four choices:
HOLD low means that no active-high bus-ownership request is being made.
READY low means that the addressed device is not yet ready and the current machine cycle must be extended.
HOLD high requests bus ownership for DMA; it leads to HOLD acknowledgement and bus release, not cycle extension.
READY high tells the processor that the addressed device can complete the transfer at normal timing.
Result
Therefore, the wait state is produced by lowering the READY input.