INFICON STM-1 Thin Film Deposition Monitor - Manual (Page 5)

2. Communications
2.1 Protocol Structure:
The protocol used to interface with the STM-1 is a byte-packet protocol. A packet begins with ASCII STX (hex 02 or decimal 2)
and ends with ‘\r’ (carriage return). 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. The structure of the packet is below:
<STX><ADDR><CMD_RSP>[<DATA>…]<CKSUM1><CKSUM2><CR>
STX: Start of text character (hex 02). Multiple STX characters in a row are allowed.
Similarly, any data between STX characters is ignored. A single STX character syncs the receiver up to receive a new message,
purging any data collected since the last STX character or carriage return received.
ADDR: Address field. This is a one-byte field. Valid ranges of a valid address are 10 hex to FE hex (16 to 254 decimal).
Addresses less than 10 hex are not allowed as they may be mistaken for framing characters. An address of FF hex is reserved as it
is used as an extension (to indicate another byte of address information follows) for products that have an address range higher
than an address of FE hex. This is for future expansion and is not used at this time.
CMD_RSP: Command/Response field. When sending a packet to the STM-1, RSPF bit is zero and the
RSP field (3 bits) is zero. When a packet is coming from the STM-1, CMD bits are the same as in the message that it was sent,
but the RSP field will be non-zero (indicating actual unit response status). This allows the direction to be positively indicated, as
well as the command preserved on the return reply.
Format of the CMD_RSP byte:
D7 D6 D5 D4 D3 D2 D1 D0
CMD3 CMD2 CMD1 CMD0 RSPF RSP2 RSP1 RSP0
CMD: Command. These are the commands that can be issued to the STM-1.
CMD
Dec/Hex Mnemonic Meaning
0/0 ----------- Cannot be used, byte could be mistaken for framing char.
1-2/1-2 Reserved Reserved for future use in protocol stack.
3/3 Prod_id Sycon product id, returned as decimal string.
4/4 Version Request slave to return software version string.
5/5 Reset Request slave to reset.
6/6 AckPF Request slave to clear RSPF bit/flag.
7/7 PROTV Request slave to return protocol stack version. Decimal string.
8/8 RndRead Random query of database, data in raw format.
9/9 RndWrit Random update of database, data in raw format
10/A Lock Lock database. Multiple locks not harmful but not nested
11/B Unlock Unlock database. Multiple unlocks not harmful but not nested.
12/C AscRd Random query of database, data in ASCII format.
13/D AscWr Update of database, data in ASCII format.
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