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5.4.1
Automatic Baud Rate Identification
The VPC3+S starts searching for the transmission rate using the highest
baud rate. If no SD1 telegram, SD2 telegram, or SD3 telegram was
received completely and without errors during the monitoring time, the
search continues using the next lower baud rate.
After identifying the correct baud rate, the VPC3+S switches to the
BAUD_CONTROL state and observes the baud rate. The monitoring time
can be parameterized (WD_BAUD_CONTROL_Val). The watchdog uses a
clock of 100 Hz (10 ms). Each telegram to its own Station_Address
received with no errors resets the Watchdog. If the timer expires, the
VPC3+S switches to the BAUD_SEARCH state again.
5.4.2
Baud Rate Monitoring
The detected baud rate is permanently monitored in BAUD_CONTROL.
The Watchdog is triggered by each error-free telegram to its own
Station_Address. The monitoring time results from multiplying twice
WD_BAUD_CONTROL_Val (user sets this parameter) by the time base (10
ms). If the timer expires, WD_SM again goes to BAUD_SEARCH. If the
user uses the DP protocol (DP_Mode = 1, see Mode Register 0), the
watchdog is used for the DP_CONTROL state, after a Set_Prm telegram
was received with an enabled response time monitoring (WD_On = 1). The
watchdog timer remains in the baud rate monitoring state when the master
monitoring is disabled (WD_On = 0). The DP_SM is not reset when the
timer expires in the state BAUD_CONTROL. That is, the DP-Slave remains
in the DATA-EXCH state, for example.
5.4.3
Response Time Monitoring
The DP_CONTROL state serves as the response time monitoring of the
DP-Master (Diag_Master_Add). The used monitoring time results from
multiplying both watchdog factors and then multiplying this result with the
time base (1 ms or 10 ms):
T
WD
(See byte 7 of the Set_Prm telegram.)
The user can load the two watchdog factors (WD_Fact_1 and WD_Fact_2)
and the time base that represents a measurement for the monitoring time
via the Set_Prm telegram with any value between 1 and 255.
EXCEPTION:
The WD_Fact_1 = WD_Fact_2 = 1 setting is not allowed. The circuit
does not check this setting.
A monitoring time between 2 ms and 650 s - independent of the baud rate -
can be implemented with the allowed watchdog factors.
VPC3+S User Manual
Copyright © profichip GmbH, 2012
= WD_Base * WD_Fact_1 * WD_Fact_2
Revision 1.04
ASIC Interface 5
39
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