The command library V1.1 generates two standard libraries in STEP 7-Micro/WIN: USS protocol library: The expanded USS protocol library for direct control of the Siemens Micromaster frequency converters MM3, MM4 & SINAMICS. Communication with the drives takes place through the USS protocol which is integrated in the Micromasters as standard. At the same time, current status values are communicated from the drive to the controller. A PROFIBUS cable is all that is required to wire up the drives & the controller. This reduces the work involved in wiring the system, saves inputs & outputs & makes initial startup easier. MODBUS protocol library: The additional MODBUS protocol library permits easy communication with the MODBUS master devices by using special communication commands & interrupt routines, which are purpose-built for MODBUS communication. Using the MODBUS slave protocol commands the S7-200 can operate as a MODBUS RTU slave in a suitable MODBUS network & communicate with MODBUS masters.