There is a Siemens software add on that gives you ModBus libraries in Micro-Win. It doesn't shoe Master in the description but I have the library and there is a master library included. Their info below:
SIMATIC STEP7-MICRO/WIN ADD ON: INSTRUCTION LIBRARY V1.1 (USS + MODBUS), FOR STEP7 MICRO/WIN V3.2 AND STEP7 MICRO/WIN V4.0, ON CD-ROM, INCL. ONLINE DOC
Part No. 6ES7830-2BC00-0YX0
This CD adds instruction libraries to the standard STEP-7 Micro/WIN Version 3.2 programming software. This new Micro/WIN Add-On Instruction Library adds two library folders to the STEP 7-Micro/WIN for the following communication protocols:
USS Protocol: The newly improved USS protocol library supports both the Micro-Master 3 (MM3) and Micro-Master 4 (MM4) drives. The USS protocol library makes controlling Micro-Master drives easier by including pre-configured subroutines and interrupt routines that are specifically designed for using the USS protocol to communicate with the drive. With the USS instructions, you can control the physical drive and the read/write drive parameters.
MODBUS® Protocol: The additional MODBUS® protocol library makes communicating to MODBUS® master devices easier by including pre-configured subroutines and interrupt routines that are specifically designed for MODBUS® communication. With the MODBUS® slave protocol Instructions, you can configure the S7-200 to act as a MODBUS® RTU slave device and communicate to MODBUS® master devices.
For customers who previously installed the previous Version 1.0 Toolbox CD library to their STEP 7-Micro/WIN32: upgrading your STEP-7 Micro/WIN32 from Version 3.x to Version 3.2 will automatically upgrade your libraries WITHOUT having to purchase the new Instruction Libraries CD. Therefore, customers only need to purchase the Instruction Libraries CD once, and all subsequent Micro/WIN V3.2.x Instruction Libraries that are released for the CD will be freely available with their next Micro/WIN V3.2.x upgrade.
