SEMI Equipment Communications Standard II

SECS-I and HSMS outline how the communication takes place (such as over RS-232C or Ethernet), SECS-II defines the format and content of messages that can be sent over SECS-I/HSMS.

The SECS II explains the message structure between equipment and host. SEMI E5 standard is a large library of messages – a few of which have redundant functions with different message structures. Most equipment supports a limited subset of these messages. Some equipment defines custom SECS-II messages that are not part of the SEMI E5 standard.

GEM standard requires only a few subsets of messages. Few SECS-II message transactions can be initiated by the Host and few can be initiated by equipment. And few may be initiated either by host or equipment. SECS 2 messages should have the correct party and correct message format as defined by E5.

Custom messages can be supported to incorporate custom features for the formats which are not defined in SEMI E5 if agreed by both the host and equipment. SECS-II messages are categorized into streams, which are identified by an integer within the range of 0 and 255 Primary Messages are odd-numbered functions and Secondary Messages are the corresponding even-numbered function. In most of the messages transmissions, either the host or equipment sends a primary message; the response is the corresponding secondary message.

Only if the reply bit is clear, a primary message should always be responded to with the complementary secondary message. A secondary Reply message is required for most of the SECS2 messages. For example, if the host sends an S1, F1 (stream1, function1) message to request ‘Are you there?’, then the equipment will send a reply S1, F2 message to indicate ‘I am here. Every Single SECS-II message exchange has a distinct transaction ID number. The standards allow message incorporation where there is more than one open, parallel transaction.

SECS-II standard also defines lists of valid data types listed below:

It’s a very efficient means to package information across any network without wasting bandwidth. When using the SECS-I standard, RS-232 serial communication, the message size is limited to 7995148 bytes (about 8 MB). When using the HSMS standard, TCP/IP network communication, the maximum message size is – 4294967295 bytes (about 4.3 GB). The structure of each standard SECS-II message is well-defined by the SEMI E5 SECS-II standard. A message can either be a simple data element, such as a binary response or an ASCII string. A message can also be a complex list structure with multiple levels of lists in the hierarchy. The SECS-II standard limits a single element within a SECS-II message to 16777215 bytes (about 16.5 MB).

SECS-II standard also defines lists of valid data types listed below: