SCU-801 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 46 - 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 47 - 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 48 - Example of command sending during answer data reply
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