Edwards SCU-350 Series

SCU-350 Series Control Unit for Turbomolecular Pump
MT-21E-201-E
Page 65
5
SERIAL COMMUNICATION PROTOCOL
5.3 Serial Protocol
5.3.1 Overview
The serial protocol used on the SIM is called Query-Command. The serial link and operations
remotely controlled can be confirmed on the PC (Personal computer).
The SIM replies the value when receiving the query.
The SIM operates according to the command when receiving it, and returns a message indicating
whether the command is valid or not.
1. QUERY/ COMMAND 2. REPLY
Figure 39 - Serial protocol on the STP
5.3.2 Sending a command or query to the SIM
Each command or query is sent to the SIM via the Serial Interface Cable, as a text message - a
sequence of ASCII coded characters.
The first character of the text message is "!" for a command, or "?" for a query. The next characters
are the mnemonic representation of the particular query or command, followed by other data if
required. The last character must be a carriage return CR (ASCII chars 13 [0D
hex
]).
The input buffer for Query-Command may be reset at any time by sending a "/" character (ASCII chars
47 [2F
hex
]). The system then ignores any previous sent characters that have not been processed. This
should be used to reset Query-Command at the beginning of the control program, rather than by
sending CR, which resets by copying the current contents of the input buffer to query or command for
execution.
Spaces can be added to improve readability or make queries/commands fixed length.
Note: Put the delay (10 ms or more) between the characters. The command cannot be received at
short delays. In this case, the error message replies. Refer to Section 5.4.2 for details