Siemens SPC3 Specifikace stáhnout pdf (Strana 63)

DPC31 HW

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DPC31 HW Description

Version V1.0 Page 61

7.5.2.4 Interface Signals

Pin Name Signal Name Input=I

Output=O

Comment

TXD_TXS

RXD_RXS

RTS_TXE

XCTS_RXA

TxS (TxS_IM)

RxS (RxS_IM)

TxE

RxA

Send signal

(for asyn. physics TxD)

Receive signal

(for asyn. physics RxD)

Enable of the send drivers/addition signal

(for asyn. physics

RTS)

Auxiliary signal for receive

(has not been needed so far in the syn. physics unit (apply to GND); for

asyn. physics XCTS)

Figure 7.5-12:

Synchronous PROFIBUS Interface of the DPC31

In the test mode, all outputs are switched to high resistance.

7.6 DPS Watchdog Timer

7.7 Watchdog Timer

7.7.1 Automatic Baudrate Detection

The DPC31 is able to recognize the baudrate automatically. The “Baud_Search” mode is entered after each

RESET as well as after the expiration of the Watchdog(WD) timer in the ‘Baud_Control’ mode.

The DPC31 starts the search for the set baudrate always with the highest baudrate. If during the monitoring

time no SD1, SD2, or SD3 message has been received completely and faultlessly, the search is continued

with the next lower baudrate.

After detecting the correct baudrate, the DPC31 switches to the “Baud_Control” mode and monitors the

baudrate. The monitoring time can be parameterized (WD_Baud_Control_Val). The watchdog processes in

this case with a clock of 100 Hz (10 msec). Each faultlessly received message to its own station address

resets the watchdog. If the timer expires, the DPC31 reswitches to the Baud_Search mode.

7.7.2 Baudrate Monitoring

In ‘Baud_Control’, the baudrate that was found is monitored

continuously

. With each faultless address to

the DPC31s own station address, the watchdog is reset. The monitoring time is the result of multiplying

‘WD_Baud_Control_Val’ (to be parameterized by the user) by the time base (10 ms). If the monitoring time

expires, the WD_SM reenters ‘Baud_Search’. If the user handles

the DP protocol with the DPC31

(DP_Mode =1; refer to Mode Register 0), the watchdog is used for the ‘DP_Control’ mode after a ‘Set_Param

message’ with enabled response monitoring ‘WD_On = 1’ was received. If the master monitoring ‘WD_On =

0’ is switched off, the watchdog timer remains in the baudrate monitoring mode. The PROFIBUS DP state

machine is not reset if the timer expires; that is, the slave remains in the DATA_EXchange mode.

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