L9779WD Datasheet, PDF (125/170 Pages) STMicroelectronics – Multifunction IC for engine management system

L9779WD
Functional description
6.17.5
MicroSecond Channel activity watchdog
MSC data frames are monitored to be sent in intervals shorter than tMSC_mon. If L9779WD
receives no valid data frame for longer than tMSC_mon, it will switch off all the drivers and
the error flag (TRANS_F) and OUT_DIS will be set.
The MRD and OUT13, 14, 21 and 25 (if low battery function is enabled) are not disabled by
missing activity on MSC.
No reset request is sent to the smart reset function module.
To enable the outputs again, the µC has to read the TRANS_F and then send the command
START, and then outputs are reactivated with the first correct data frame. If the fault flag is
not cleared the START command is ignored.
By default the MicroSecond Channel activity watch dog is enabled and the monitoring time
will start after writing of the OUT_DIS bit by START command. Each time the L9779WD
receives a valid data frame the tMSC_on timer is reset. This means that micro controller can
drive the outputs only when the monitoring module is active.
To disable the MicroSecond Channel activity watch dog the µC have to set to 0 the bit
MSC_ACT_EN.
If the MSC frame has a wrong number of bit the flag TRANS_L is set but no action on
outputs is taken. The frame with wrong length is ignored.
Table 58. MicroSecond Channel activity watchdog
Symbol
Min
Typ
Max
Unit
tMSC_mon
100
142
185
µs
-30%
0.9*t2WD
+30%
ms
-30%
0.8*t2WD
+30%
t1_WD
-30%
0.7*t2WD
+30%
-
-
0
-
14
20
26
35
50
65
t2_WD
59
70
ms
91
70
100
130
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