How to allow 2 Modbus Masters to communicate to multiple Modbus slaves (Part 1 Overview)

Modbus is simple to understand and offers great flexibility as it can be used over RS 232 and RS485 multidrop. However unlike it's more powerful cousin Profibus DP it does not allow two masters to communicate to one slave at the same time, as it does not support acyclic communications. This becomes an issue if we want to use SIMATIC PDM and require connectivity to IOT applications.
I will demonstrate over the next three videos how to overcome this issue.