What is SECS/GEM?

1. SECS (SEMI Equipment Communication Standards) and GEM (Generic Model For Communications and Control Of Manufacturing Equipment) standard is published and maintained by SEMI.org, an international organization of semiconductor manufacturers, is an organization body that governs the standard for semiconductor manufacturing.
2. It is the main communication protocol used in automation for (initially) semiconductor/electronics industries, however, today it has been widely adopted in photovoltaic and SMT industries too.
3. It provides a communication interface between equipments and host systems.
4. Unlike other communication protocol like PLC, it enable equipments from variety of vendors to communicate using standard and consistent protocol with various type of Host systems. 

 To understand the SECS/GEM standards you will need to purchase the following 3 basic standards from SEMI:  

1. SEMI E30 GEM Standard - This is the "Brain" that defines the behaviours of equipment (Business Rules), state machine and some rules like which SECS-II messages should be used, in what situations, and what the resulting activity should be. It also defines the functionalities like Status Data Collections, Trace Data Collection, Alarms Management, Spooling, Remote Command, etc.
2. SEMI E5 SECS-II - Defines the details of the interpretation of messages (APIs) exchanged between equipment a host. It also defines message inputs/outputs data structure, data item format, acknowledgement codes, etc.
3. SEMI E37 HSMS - High Speed SECS Message Services. This is a transport layer based on TCP/IP protocol and a successor of the previous SEMI E4 SECS-I standard that is based on serial communication. This is also the layer where the SECS-II messages are encoded into HSMS message format.