In this initial power on mode, the FIT is just monitoring FC/SA bus communications
and is not actively participating in communications.
The Bus Health consists of eight bars indicating the health of the FC/SA
communication bus. The higher number of bars the higher the health. When the FIT
is first connected to the bus, the Bus Health starts out at eight bars and then the
communications are monitored for errors. The number of bars is reduced if
communication errors are occurring. Communication errors can occur for various
reasons such as noise from electrical sources, long wire lengths, heavily loaded buses,
loose terminations, duplicate addresses, or improperly wired buses. Some
communication errors are tolerated as long as they do not cause issues such as
controllers going online and offline, erratic communications, or poor system control.
A Bus Health reading of eight bars is obviously desired, but it is considered
acceptable to have a Bus Health reading of four bars or more. Bus Health is basically
calculated by counting communication errors over time. A Bus Health of four bars
equates to two communication errors per minute, which is tolerable for FC/SA
communications.
When the FIT powers on, it may display No MSTP. This can mean the FIT is seeing
bus traffic, but a token is not passing between addresses. This occurs when one or
multiple FEC/VMA controllers on the bus have an address switch position eight
(normally labeled 128) in the ON position. This switch is not to be used on a hard-
wired Johnson Controls MS/TP Bus. It is reserved for Wireless bus installations. If you
see this condition, validate that all FEC/VMA MS/TP hard-wired controllers have the
128 switch in the OFF position.
No MSTP can also be displayed if an MS/TP bus which is active has installation errors
significant enough for the FIT to fail determining a baud rate. If this condition is
experienced, use the FIT’s Voltage > IdleBus to validate proper voltages (see Voltage
Levels for more information). In addition, the FIT’s baud rate could be adjusted from
the default autobaud in the System Menu to the specific baud rate of the bus that is
being tested (see System Menu for more information).
FIT Issues Menu
The Issues menu reports on any bus errors or other issues that are occurring on the
FC/SA bus the FIT is monitoring. The FIT is constantly monitoring the FC/SA bus for
errors. Only the last five communication errors are reported in the issue menu and
the FIT continues to update the number of issues during an MS/TP validation session.
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