UMAX090600 Version 1
Preliminary Documentation – May be Subject to Change
15-48
Function Block
Minimum Threshold
Maximum Threshold
Thermistor Input
Minimum Error
Maximum Error
Battery Voltage
Battery Undervoltage Threshold Battery Overvoltage Threshold
Power Supply
Power Undervoltage Threshold
Power Overvoltage Threshold
Over Temperature
N/A
Over Temperature Shutdown
Lost Communication
N/A
Received Message
Timeout
(any)
Table 3: Fault Detection Thresholds
When applicable, a hysteresis setpoint is provided to prevent the rapid setting and clearing of the
error flag when an input or feedback value is right near the fault detection threshold. For the low end,
once a fault has been flagged, it will not be cleared until the measured value is greater than or equal
to the Minimum Threshold
+ “Hysteresis to Clear Fault.”
For the high end, it will not be cleared
until the measured value is less than or equal to the Maximum Threshold
– “Hysteresis to Clear
Fault.”
The minimum, maximum and hysteresis values are always measured in the units of the fault
in question.
The next setpoint in this function block is the
Event Generates a DTC in DM1.
If and only if this is
set to true will the other setpoints in the function block be enabled. They are all related to the data
that is sent to the J1939 network as part of the DM1 message, Active Diagnostic Trouble Codes.
A Diagnostic Trouble Code (DTC) is defined by the J1939 standard as a four-byte value which is a
combination of:
SPN
Suspect Parameter Number (first 19 bits of the DTC, LSB first)
FMI
Failure Mode Identifier
(next 5 bits of the DTC)
CM
Conversion Method
(1 bit, always set to 0)
OC
Occurrence Count
(7 bits, number of times the fault has happened)
In addition to supporting the DM1 message, the CAN-BC-LED Controller also supports
DM2
Previously Active Diagnostic Trouble Codes
Sent only on request
DM3
Diagnostic Data Clear/Reset of Previously Active DTCs
Done only on request
DM11
Diagnostic Data Clear/Reset for Active DTCs
Done only on request
So long as even one Diagnostic function block has Event Generates a DTC in DM1 set to ‘True’, the
CAN-BC-LED Controller will send the DM1 message every one second, regardless of whether or
not there are any active faults, as recommended by the standard. While there are no active DTCs,
the CAN-BC-LED will send the “No Active Faults” message. If a previously inactive DTC becomes
active, a DM1 will be sent immediately to reflect this. As soon as the last active DTC goes inactive,
it will send a DM1 indicating that there are no more active DTCs.
If there is more than one active DTC at any given time, the regular DM1 message will be sent using
a multipacket Broadcast Announce Message (BAM). If the controller receives a request for a DM1
while this is true, it will send the multipacket message to the Requester Address using the Transport
Protocol (TP).
When the fault is linked to a DTC, a non-volatile log of the occurrence count (OC) is kept. As soon
as the controller detects a new (previously inactive) fault, it will start decrementing the “
Delay Before
Sending DM1
” timer for that Diagnostic function block. If the fault has remained present during the
delay time, then the controller will set the DTC to active, and will increment the OC in the log. A DM1
