FIT
Display
Installation
Problem
Idle Bus Voltage
Symptom
FIT Issues
Menu Resolution Process
+ and COM
are
swapped
All the readings
are trying to go to
0 VDC.
ChrFrame Zero or few controller
addresses are
reporting.Split the bus in
half and test each segment
individually. Continue this
process with smaller
segments until the issue is
found.
Keep in mind the following:
The further away from a problem the FIT is positioned, the reduced effect on a
reading that problem may have.
Each bus segments Idle Bus Voltage must be read independently. It cannot be
read across repeaters.
Proper EOL Termination
It is recommended that most FCBs should have an EOL termination set on each
controller at the end of each bus segment. Proper EOL termination is needed for
reliable communications. The FIT tool has an EOL termination circuit that can be
turned On or Off by the user. See Table 7 for the EOL switch positioning.
Table 1. EOL Termination Switch Positions
Mode Switch Position
1-ON-1 Mode EOL circuit is On.
Monitor Mode EOL circuit is Off.
Scan Bus Mode EOL circuit is Off.
The user can override the EOL operation by using the EOL Command under the
System menu. If the supervisory controller is not connected to the bus, use the FIT to
start communications in Scan Bus mode.
If the FIT is connected at the end of the bus where the supervisory
controller would be and the supervisory controller was an EOL, then it would be
advisable to set the EOL switch to On in the FIT System menu.
The bus is now properly terminated as if the supervisory controller was in place. The
EOL On command allows the FIT to act as an active termination that can be placed
anywhere on the bus to help troubleshoot bus communication issues.
Keep in mind the FCB EOL termination attribute is limited to Johnson Controls
manufactured products that have a built-in EOL switch. The location of other EOL
Note:
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