How does PF value affect PGN addressing in NMEA 2000?

How does PF value affect PGN addressing in NMEA 2000?

• A. PF determines how data is encoded; PS determines error checking.
• B. PF determines message length only; PS is unused.
• C. PF < 240 indicates PDU1 with destination address in PS; PF ≥ 240 indicates PDU2 broadcast.
• D. PF < 240 indicates broadcast; PF ≥ 240 indicates destination address.

Answer: (C)

PF is the PDU format that tells how the PGN is addressed on the CAN bus. When PF is less than 240, the message uses PDU1 format, and the PDU Specific field carries the destination address, so the PGN is targeted to a single device. When PF is 240 or greater, the message uses PDU2 format, the PS field becomes a group extension that's part of the PGN, and there is no single destination address—the message is broadcast to all nodes that listen for that PGN. That’s why this addressing rule is correct: PF < 240 means a specific destination in PS; PF ≥ 240 means a broadcast with PS acting as part of the PGN rather than a destination. The other statements misstate what PF and PS control or reverse the roles of PDU1 and PDU2.

PF is the PDU format that tells how the PGN is addressed on the CAN bus. When PF is less than 240, the message uses PDU1 format, and the PDU Specific field carries the destination address, so the PGN is targeted to a single device. When PF is 240 or greater, the message uses PDU2 format, the PS field becomes a group extension that's part of the PGN, and there is no single destination address—the message is broadcast to all nodes that listen for that PGN. That’s why this addressing rule is correct: PF < 240 means a specific destination in PS; PF ≥ 240 means a broadcast with PS acting as part of the PGN rather than a destination. The other statements misstate what PF and PS control or reverse the roles of PDU1 and PDU2.