MVI46-PDPS ♦ SLC Platform
Diagnostics and Troubleshooting
Profibus DP Slave Communication Module
User Manual
ProSoft Technology, Inc.
Page 32 of 53
The SPC3 is able to identify the baud rate automatically. The "baud search" state is
located after each RESET and also after the watchdog (WD) timer has run out in the
"Baud_Control_state." As a rule, SPC3 begins the search for the set rate with 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 with the
next lowest baud rate.
After identifying the correct baud rate, SPC3 switches to the "Baud_Control" state and
monitors the baud rate. The monitoring time can be parameterized
(WD_Baud_Control_Val). The watchdog works with a clock of 100 Hz (10 milliseconds).
The watchdog resets each telegram received with no errors to its own station address. If
the timer runs out, SPC3 again switches to the baud search state.
Further explanation of Status Register [0]: Word 9 Bit states
Bit 0
Offline/Passive-idle
0 = SPC3 exits offline and goes to passive-idle. The idle timer and Wd timer go
offline.
1= SPC3 exits offline and goes to passive-idle. The idle timer and Wd timer are
started.
Bit 4, 5
10 = Data Exchange State is Normal. The SPC3 has a correct configuration.
Bits 6, 7
Watchdog Timer
Automatic Baud Rate Identification
The SPC3 is able to identify the baud rate automatically. The "baud search" state is
located after each RESET and also after the watchdog (WD) timer has run out in the
"Baud_Control_state." As a rule, SPC3 begins the search for the set rate with 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 with the
next lowest baud rate.
After identifying the correct baud rate, SPC3 switches to the "Baud_Control" state and
monitors the baud rate. The monitoring time can be parameterized
(WD_Baud_Control_Val). The watchdog works with a clock of 100 Hz (10 milliseconds).
The watchdog resets each telegram received with no errors to its own station address. If
the timer runs out, SPC3 again switches to the baud search state.
Baud Rate Monitoring
The located baud rate is constantly monitored in "Baud_Control." The watchdog is reset
for each error-free telegram to its own station address. The monitoring time results from
multiplying both "WD_Baud_Control_Val" (user sets the parameters) by the time base
(10 ms). If the timer expires, WD_SM again goes to "Baud_Search". If the user carries
out the DP protocol (DP_Mode = 1, see Mode register 0) with SPC3, the watchdog is
used for the "DP_Control" state, after a "Set_Param telegram" was received with an
enabled response time monitoring "WD_On = 1." The watchdog timer remains in the
baud rate monitoring state when there is a switched off "WD_On = 0" master monitoring.
The PROFIBUS DP state machine is also not reset when the timer runs out. That is, the
slave remains in the DATA_Exchange state, for example.
