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?

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:

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