INFICON STM-1 Thin Film Deposition Monitor - Manual (Page 6)

RSP: Once the packet is sent, the STM-1 receives and acknowledges the packet, and sends its response. In the CMD_RSP byte,
the CMD bits are unchanged from the master, but the RSP bits are filled in according to the status of the slave. See table below.
RSP
Mnemonic Meaning
0 ------------- Response code must be non-zero, to indicate direction.
1 OK Command understood and executed.
2 Err_inv_cmd Illegal command (CMD code not valid).
3 Err_syntax Syntax error. (Too many bytes in data field, not enough bytes, etc).
4 Err_range Data range error.
5 Err_inhibited Inhibited
6 Err_obso Obsolete command. No action taken, but not really an error.
7 Reserved for future protocol stack use
Because there are multiple errors possible, but limited RSP codes, the following table describes the RSP code returned for
database transaction errors:
Database transaction: Address to read/write is invalid. Err_syntax
Database transaction: Attempt to write a read only record. Err_syntax
Database Transaction: Attempt to write to the configuration parameters group while a commit or rollback
operation is pending, or an attempt to query configuration parameters group while a rollback was pending. Err_inhibited
Database transaction: An attempt to write to a semaphore register while flags still pending. Err_inhibited
Database transaction: Number of bytes to write does not match record length. Err_syntax
Database transaction: Update data value out of range Err_range
Database transaction: Update data, ASCII mode, or data malformed. Err_syntax
RSPF: This bit only has meaning when a packet is coming from the STM-1. If this bit is 1, then the slave has been reset since the
last AckPF power fail acknowledgement was received.
DATA: The optional data. Interfacing with the STM-1 is done by querying and setting records in the database on the STM-1 card.
Information about this database is provided in the Data Access section 2.2, and information on how the data field is formed in
both outgoing and incoming packets is contained in section 2.3, Forming the Data Field.
Since this protocol is binary transparent, STX and carriage return characters are not allowed in the data field. To solve this
problem, these characters must be escaped. To send a hex 02, send the protocol escape character (HEX 07) followed by ‘0’ (hex
30). To send a hex 0D, send the protocol escape character (HEX 07) followed by ‘1’ (hex 31). To send a hex 07, send the protocol
escape character (HEX 07) followed by ‘2’ (hex 32). Note that the protocol escape character (HEX 07) cannot be sent by itself,
but can only be sent followed by a 0,1,or2. If the protocol escape character is sent by itself, or is not followed by a 0,1,or 2, then
the packed is deemed invalid and ignored.
CKSUM1, 2: The checksum characters for the message. This is the mod-256 checksum of all packet bytes except the STX and
carriage return BEFORE ESCAPE CHARACTER BYTE STUFFING. The data is encoded as follows:
Compute the mod 256 checksum of ADDR, CMD_RSP and DATA fields, before byte stuffing with escape characters.
CKSUM1 character is the upper (most significant) four bits of the checksum (read as a nibble, 0-15, or right justified) plus hex 30
(ASCII 0). This yields an ASCII character from ‘0’ (hex 30) to ‘?’ (hex 3f).
CKSUM2 character is the lower (least significant) four bits of the checksum plus hex 30 (ASCII 0). This yields an ASCII
character from ‘0’ (hex 30) to ‘?’ (hex 3f).
Note 2.1: Invalid packets (bad checksum, too short, corrupt data, bad escape sequences) are ignored by the STM-1. That means
there is no reply at all to an invalid packet.
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