Chapter 5 communication, 1 communication protocol, 2 sycon multi-drop protocol (smdp) – INFICON STM-2 USB Thin Film Rate/Thickness Monitor User Manual
Page 69: 1 command format, Chapter 5
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STM-2 Operating Manual
Chapter 5
Communication
5.1 Communication Protocol
Although STM-2 connects via USB, it integrates as a virtual serial port. Therefore,
STM-2 may be opened, read from, and written to just like any serial port. STM-2
follows the SMDP (Sycon Multi Drop Protocol), which makes it possible to
communicate with STM-2 without following USB protocol (see
).
If custom software will be developed on Windows, INFICON provides an ActiveX
control that implements the SMDP protocol and manages the serial ports, allowing
multiple programs to access the same STM-2. For more information concerning
ActiveX and SMDP, contact INFICON (refer to
).
5.2 Sycon Multi-Drop Protocol (SMDP)
SMDP is a byte-packet, binary protocol. All eight bits of the data of a byte/character
are used. Standard asynchronous serial conventions apply. A packet begins with
STX (ASCII 0x02) and ends with CR (carriage return, 0x0D).
The SMDP specification provides several common, mandated command codes.
STM-2 responds to these common messages. For example, the reset command
will cause STM-2 to reboot, as though power was cycled. This will set STM-2 into
a known state. Another common command queries the product type or ID. This
command (0x30) will return an ASCII integer code that identifies the product type
(see
). This allows a master computer to poll a network
and locate devices by their types and ensure that the proper connection and
commands are used for the appropriate product.
NOTE: Each field in angle brackets (< >) is a byte, and is not optional. Fields in
regular brackets ([ ]) are optional. Ellipses (...) mean one or more of the
previous.
5.2.1 Command Format
<STX><ADDR><CMD_RSP>[<DATA>...]<CKSUM1><CKSUM2><CR>
STX . . . . . . . . . . . . . . . . . . . . . . . . . Start of text character (hexadecimal 02)
Multiple STX characters in a row are allowed.
Data between STX characters is ignored. A
single STX character initializes the receiver
to receive a new message, purging any data
collected since the last STX character or
carriage return received.