If a system requires only 32 codes for identification, which SIF mode is designated for this limit?

• A. Mode 3A
• B. Mode 2
• C. Mode 1
• D. Mode 4

Answer: (C)

SIF modes control how identification information is transmitted and how many unique IDs can be sent in a reply. When a system only needs a small set of IDs, you want a mode that uses a compact identification field, so there are enough distinct codes without wasting space. For 32 distinct codes, you need 5 bits of information, since 2^5 equals 32. The mode designed to support such a small, fixed set of identification codes is the one that uses that 5-bit field. That makes it the designated choice for a limit of 32 codes.

Other modes are built for larger identification spaces or different purposes. For example, Mode 3A carries a much larger code space (four octal digits), Mode 4 uses encrypted authentication, and Mode 2 uses its own scheme with more identifiers than a 5-bit field allows. So, when the requirement is specifically 32 codes, the mode with the 5-bit, up-to-32-ID capability is the best fit.