UMAX140610. LIN
– J1939 CAN Protocol Converter with PWM Output. Version 1
Page: 55-81
At power up, the DM1 message will not be broadcasted until after a 5 second
delay. This is done to prevent any power up or initialization conditions from
being flagged as an active error on the network.
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 will immediately be generated that includes the new DTC. The timer
is provided so that intermittent faults do not overwhelm the network as the fault comes and
goes, since a DM1 message would be sent every time the fault shows up or goes away.
The Diagnostic function block has a setpoint
“Event Cleared only by DM11.”
By default, this
is always set to False, which means that as soon as the condition that caused an error flag to
be set goes away, the DTC is automatically made Previously Active, and is no longer included
in the DM1 message. However, when this setpoint is set to True, even if the flag is cleared, the
DTC will not be made inactive, so it will continue to be sent on the DM1 message. Only when a
DM11 has been requested will the DTC go inactive. This feature may be useful in a system
where a critical fault needs to be clearly identified as having happened, even if the conditions
that caused it went away.
In addition to all the active DTCs, another part of the DM1 message is the first byte which
reflects the Lamp Status. Each Diagnostic function block has the setpoint
“Lamp Set by
Event in DM1”
which determines which lamp will be set in this byte while the DTC is active.
The J1939 standard defines the lamps as
‘Malfunction’, ‘Red, Stop’, ‘Amber, Warning’
or
‘Protect’.
By default, the
‘Amber, Warning’
lamp is typically the one set by any active fault.
By default, every Diagnostic function block has associated with it a proprietary SPN. However,
this setpoint
“SPN for Event used in DTC”
is fully configurable by the user should they wish it
to reflect a standard SPN define in J1939-71 instead. If the SPN is changed, the OC of the
associate error log is automatically reset to zero.
Every Diagnostic function block also has associated with it a default FMI. The only setpoint for
the user to change the FMI is
“FMI for Event used in DTC,”
even though some Diagnostic
function blocks can have both high and low errors as shown in Table 30. In those cases, the
FMI in the setpoint reflect that of the low end condition, and the FMI used by the high fault will
be determined in the table below. If the FMI is changed, the OC of the associate error log is
automatically reset to zero.
Table 33. Low Fault FMI versus High Fault FMI
FMI for Event used in DTC
– Low Fault
Corresponding FMI used in DTC
– High Fault
FMI=1, Data Valid But Below Normal
Operational Range
– Most Severe Level
FMI=0, Data Valid But Above Normal
Operational Range
– Most Severe Level
FMI=4, Voltage Below Normal, Or Shorted
To Low Source
FMI=3, Voltage Above Normal, Or Shorted
To High Source
