. If theseoptional features are supported, the vendorplaces keywords indicating so in the GSD file.For example, if a device supports the setting ofits address across the bus, its GSD file willinclude an entry Set_Slave_Add_supp = 1.There is a very rudimentary motion controlcapability, to SYNChronize outputs, built intoFunctionalityA device vendor has the option of includingsome additional PROFIBUS functionality in adevice. These optional features include allowingthe setting of the device address across the bus,supporting the output SYNC feature, and supportingthe input FREEZE feature. If theseoptional features are supported, the vendorplaces keywords indicating so in the GSD file.For example, if a device supports the setting ofits address across the bus, its GSD file willinclude an entry Set_Slave_Add_supp = 1.There is a very rudimentary motion controlcapability, to SYNChronize outputs, built intothe standard DPV0 protocol. This SYNC functionalityallows, for example, a group of driveson a conveyor to be ramped up to speed in asynchronous fashion. A SYNC operation can beinitiated via an instruction in your control program(if the master supports it). This forces allthe affected devices to immediately process theBASICS OF PROFIBUS OPERATION 19last output data sent from the master forinstance, a speed and direction command. Themaster sends this SYNC command out betweenI/O cycles. While giving the drives time to rampup, your control program can write output data for example, the next speed and direction stepin the ramp-up/ramp-down to the drives in thegroup over the next few cycles, The drives ignorethe data until your control program causesanother SYNC command to be sent betweenI/O cycles. When the ramp operation is complete,your control program can cause anUNSYNC command to be sent to put the drivesin the group back into the normal mode of processingoutput data as it is received.There is also a capability for your control programto cause a group of devices to FREEZEtheir input images that are being sent back to themaster. This provides the capability to, for example,take a snapshot at a given time of severalanalog inputs distributed over several devices.Perhaps you are doing some calculations in yourcontrol program involving these analog inputvalues, and you need all the values to be frozenat the same instant. A FREEZE operation20 BASICS OF PROFIBUS OPERATIONtakes place when an instruction in your controlprogram initiates it, and these operations can beinitiated repeatedly from your program. Thedevices continue to read the field inputs but donot update the image being sent back to themaster except on a FREEZE command, which issent by the master between I/O cycles. If youwant the devices to be put back into the normalmode of continuously updating the inputs beingsent back to the master, your program can initiatean UNFREEZE command.In this chapter, we have attempted to give you aquick, general overview of the capabilities andfeatures of PROFIBUS DPV0. Now lets get intothe details of configuring the network and gettingit up and running!