FF-SIF uses the existing H1 protocol as the “Black Channel”
network between the logic solver and the SIS devices. It is
important to note that no changes were made to the fundamental
H1 protocol for implementation in SIS, but additional device diagnostic
functions and fault detection capabilities were required. In addition
to the device diagnostics, the primary advantage to using FF-SIF as the
black channel for safety applications is the network diagnostics that are
possible. Traditional analog-based networks lack the ability to detect noise,
corruption, and faults in the network.