ROM timing definition: What is meant by ROM access time in datasheets? Choose the option that correctly defines the interval from a valid address being applied to valid output data appearing at the device pins.

Introduction / Context:
Access time is a key specification for read-only memories and other asynchronous memories. It informs system designers how quickly a CPU or controller can read stable data given address setup and control signals, impacting clock frequency, wait states, and bus timing margins.

Given Data / Assumptions:

• Asynchronous ROM with address, chip enable, and output enable signals.
• Access time measured to valid logic levels at data outputs.
• Programming time is unrelated to read access performance.

Concept / Approach:
Access time is defined as the interval between a defined starting condition—typically address valid with chip enabled—and the moment when output data is guaranteed valid. ROMs are read-only in operation; “write time” is irrelevant in normal use. Precise timing paths (tAA, tCE, tOE) may be specified, but the common description aligns with option (c).

Step-by-Step Solution:
1) Apply a valid address while asserting CE and possibly OE.2) Internal decoding and sensing occur.3) After the specified interval (access time), outputs settle to valid levels.4) System can sample data safely after this time or when a ready/hold-off signal indicates readiness.

Verification / Alternative check:
Open any ROM/flash datasheet and observe tACC or related parameters defined exactly as address-to-data-valid intervals.

Why Other Options Are Wrong:
Programming time is for EPROM/EEPROM write operations, not ROM access. There is no meaningful “difference between READ and WRITE times” for ROM. Address activation wording in (d) is not the standard definition.

Common Pitfalls:
Misinterpreting OE gating delays as access time alone; ignoring that multiple timing paths can qualify data validity.

Final Answer:
the time it takes to get valid output data after a valid address is applied