After programming – are PROMs functionally equivalent to mask ROMs (i.e., fixed read-only contents)?

Introduction / Context: Read-only memories come in several manufacturing/programming styles. Mask ROMs are factory-programmed during fabrication; PROMs are programmed by the user once after fabrication. This question asks whether a PROM, once programmed, behaves like a mask ROM from a system’s perspective.

Given Data / Assumptions:

• PROM = one-time programmable by blowing fuses or setting antifuses.
• Mask ROM = patterns defined in silicon masks at the factory.
• Focus on behavior after programming, not on how the pattern was created.

Concept / Approach: After a PROM is programmed, its bit pattern is fixed and read-only. The access signals, timings, and logic-level behavior mirror ROM semantics. Therefore, at runtime, a programmed PROM and a mask ROM both present immutable data to the bus and are functionally indistinguishable to the rest of the system.

Step-by-Step Solution:

Verification / Alternative check: Datasheets list PROM read timing matching ROM interfaces; system schematics swap PROM/mask ROM footprints as drop-in options in some designs.

Why Other Options Are Wrong: UV erasure applies to EPROM, not PROM. Bipolar vs CMOS technology does not change post-program read-only behavior. Refresh cycles are DRAM concerns, not ROM/PROM.

Common Pitfalls: Confusing PROM with EPROM/EEPROM; forgetting PROM is one-time programmable and not erasable.

Final Answer: Correct