2 sycon multi-drop protocol (smdp), 1 command format – INFICON STM-2XM 2-Channel Rate/Thickness Monitor User Manual
Page 86
5 - 6
PN
07
4-
61
4-
P1
A
STM-2XM Operating Manual
DATA . . . . . . . . . . . . . . . . . . . . . . . . 1 to 80 characters of data (see
for data commands).
NOTE: STX characters are not allowed in
the data field.
CKSUM . . . . . . . . . . . . . . . . . . . . . . Checksum character for the message
This is the modulo-256 checksum of data
bytes only. The checksum can be any valid 8
bit decimal, from 0 (hexadecimal 00) through
255 (hexadecimal FF) depending on the data
field contents. If this does not match the
actual checksum of the data. STM-2XM will
not respond to the command.
5.5.2 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. The link must be
configured for one start bit, eight data bits, and one or more stop bits. The logic
polarity and bit order adopt the standard used for asynchronous serial
communications (refer to
). A packet begins with STX (ASCII 0x02)
and ends with CR (carriage return, 0x0D).
The SMDP specification provides several common, mandated command codes.
STM-2XM responds to these common messages. For example, the reset
command will cause STM-2XM to reboot, as though power was cycled. This will set
STM-2XM 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
section 5.5.2.1.2 on page 5-10
). 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.
5.5.2.1 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.