ADC0804 start-of-conversion control In the ADC0804 successive-approximation ADC, which hardware input is used to initiate (start) a conversion, assuming chip select (CS) is asserted appropriately?
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AWR line
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BCS line
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CINTR line
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DVref/2 line
Answer
Correct Answer: WR line
Explanation
Introduction / Context:The ADC0804 is an 8-bit successive-approximation ADC commonly used with microcontrollers. Knowing which control signal initiates a conversion is essential for correct timing and interfacing.
Given Data / Assumptions:
- Device: ADC0804 8-bit SAR ADC.
- Control pins include CS, RD, WR, INTR, and Vref/2.
- CS must be active (LOW) for control actions to take effect.
Concept / Approach:On the ADC0804, a LOW-going transition on WR (with CS LOW) starts the conversion process. INTR is an output that signals end-of-conversion. Vref/2 sets the analog scale; it does not start conversion. CS enables access but does not by itself trigger conversion.
Step-by-Step Solution:
1) Assert CS LOW to select the ADC.2) Pulse WR from HIGH to LOW (then HIGH) to start conversion.3) Wait for INTR to go LOW, indicating end-of-conversion.4) Read data by asserting RD as per timing requirements.Verification / Alternative check:Timing diagrams show WR falling edge as the start-conversion event; INTR transitions LOW only after conversion completes.
Why Other Options Are Wrong:
- CS line: Only selects the device; does not initiate conversion.
- INTR line: Output that indicates completion, not a start input.
- Vref/2 line: Reference-scaling input, unrelated to control flow.
Common Pitfalls:Confusing INTR (EOC) with a start pin, or forgetting CS must be active during WR.
Final Answer:WR line