Types of ROM — factory mask options Which ROM type must be custom programmed by the manufacturer during fabrication (i.e., mask-programmed)?

Introduction / Context:
Read-Only Memory (ROM) families differ in when and how the data pattern is written. Some are field-programmable; others are fixed at the factory. Understanding these differences informs cost, lead time, and flexibility in product design.

Given Data / Assumptions:

• Mask ROM is defined by photolithographic masks that include or omit connections.
• EPROM/EEPROM/Flash are field- or lab-programmable after fabrication.
• “ROM” as a generic term is ambiguous; the question targets the specific subtype requiring factory customization.

Concept / Approach:

Mask ROM content is permanent and set by the silicon masks before wafer processing. This yields very high density and low cost per unit at high volumes, but it sacrifices flexibility and requires substantial NRE (nonrecurring engineering) for masks.

Step-by-Step Solution:

Verification / Alternative check:

Device datasheets and manufacturing flows clearly distinguish mask-programmed ROM from one-time or reprogrammable ROM families.

Why Other Options Are Wrong:

• Generic “ROM” does not specify factory programming.
• EPROM and EEPROM are user-programmable after fabrication.

Common Pitfalls:

• Confusing one-time programmable (OTP) EPROM with mask ROM; OTP EPROM is field-programmable once, not mask-set at the factory.

Final Answer:

mask ROM