PROFIBUS Manual

The Set_Parameter telegram comprises no fewer than 7 and no more than 244 bytes of payload data.

 

 

The first seven parameter bytes have a mandatory specification in the standard. Bytes 8 to 10 have been codified in DP-V1. Other bytes are vendor-specific.

 

Parameters are coded according to the following pattern: X = value 1 enabled, value 0 disabled

 

 

 

The values stored in the two bytes represent factors for adjusting the watchdog time (TWD). In a DP slave, watchdog monitoring ensures that, if the DP master goes down, outputs will assume the secure state after this period has elapsed.

 

The time is calculated as follows:

 

Watchdog = factor_1 * factor_2 * 10 ms

 

In this way, times can be achieved ranging from 10 ms to 650 sec, regardless of the baud rate. With bit 2 in byte 8 this watchdog time-base can be adjusted by 1 ms. Periods 10 times shorter can therefore be set. Watchdog monitoring is switched on or off by the bit WD_On.

 

This is the minimum time that the DP slave must wait until it is allowed to send its response telegrams back to the DP master.

 

Straight DP operation:  0, 11 to max TSDR according to standard

Mixed operation (e.g. DP&FMS): 0, 11 to 255 tBit

 

With value 00 the existing value will be maintained.

 

 

The DP slave only accepts parameter telegrams if the ident number they transmit matches the slave's own ident number. Exception: The min TSDR can also be set if both the Lock_Req and Unlock_Req bits are zero and the ident numbers do not match.

 

 

This byte can be used to form groups for the Global_Control function. Each bit represents a group. It is only accepted if the Lock_Req bit is set.

 

The following bytes are extensions for DP-V1. A controller that does not support these extensions should set all these values to 0. If a device that supports these extensions sets in the GSD file the key word:

 

DPV1_Slave = 1

 

 

The key word

WD_Base_1ms_supp = 1

in the GSD file indicates whether the DP slave supports this function of the 1 ms watchdog.

 

The publisher function is explained in more detail in the section on direct data exchange  and Fail_Safe mode relates to the state of the class 1 master.

 

Check_Cfg_Mode: If this bit is at 0 the slave must verify the consistency of the Chk_Config telegrams from the DP-V1 master and reject faulty configurations. If this bit is at 1 however, vendor-specific deviations are allowed. For example, it is possible to accept a module in the configuration even though it is not currently plugged in. Support for this bit is indicated in the GSD file with the key word

Check_Cfg_Mode = 1

 

Alarms belong to the acyclic services.

 

If the Prm_Structure bit is set, this data is then followed by parameter blocks with further standardized parameters and instructions. Individual blocks and instruction groups can be enabled with individual bits.  

 

The whole block is built up in a fixed format.