The OOB comparator allows all nodes to integrate / reintegrate into the network by preventing a mixed fast and slow node collision or a false end-of-frame detection, allowing controllers to determine any ongoing activity on the bus. This avoids destructive arbitration faults. Without the OOB comparator, an integrating or reintegrating SIC mode receiver could misinterpret FAST mode data transmission as inter-frame spacing, causing it to transmit incorrectly and generate frame corruption or bus contention.

Figure 3-6 shows an example where the transmitting node is in the XL / FAST mode while the receiving node is in the SIC / slower mode. In this situation, due to signal degradation across the cables, the receiver's input thresholds (0.9V) could be higher than the bus level, causing RXD may then be permanently high. This can lead to the receiving node comprehending a permanent RXD = 1 as the end-of-frame or inter-frame spacing, and can start transmitting a new packet. This situation could lead to a collision on the bus and packet destruction. To prevent this situation, the OOB comparator implements input thresholds of -450mV to -250mV, allowing the SIC receiver to detect FAST mode data. This in turn allows the receiving node to properly integrate or reintegrate to the bus without any destructive interference to CAN XL traffic.

Figure 3-6 Out-of-Bounds (OOB) Comparator