SCU-800 Control Unit for Turbomolecular Pump
SERIAL COMMUNICATION
PROTOCOL
Always check the LRC checksum of answer data. When LRC checksum is incorrect, do not use
the data. When the incorrect data caused by noise is accepted, parameters might be set
unexpected values. In this case, the processing of the tool application may determine to be a
communication failure. When LRC checksum is incorrect, receive the answer data again
according to the following methods.
- Send "NAK" within 1500 msec after receiving the answer data, and then receive the answer
data again from SIM. However, when using RS485, send "NAK" at least 1 msec has passed
after receiving the answer data.
- Stop once the communication process, and try the communication process again.
The answer resending process by NAK sent
when LRC is incorrect value.
Figure 43 - Example of answer resending process
When sending the following command before receiving the answer data from the SIM, the
contents of the answer data and sent command from the SIM will not match.
In this case, stop the communication about approximately 5 seconds to clear all the receiving
buffer of the tool application, and then start the communication again.
It seems that different answer data from
sending command is responded.
Figure 44 - Example of response when the command is sent continuously
In addition, when using RS485, do not send commands while the answer data is sent from the
SIM. The crosstalk of sending data and receiving data will occur, and it causes communication
failure such as a flaming error.
When using RS485, the crosstalk is happened if the
next command is sent during an answer data reply.
Figure 45 - Example of command sending during answer data reply
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