STP-iXA4507 series Turbomolecular Pump
SERIAL COMMUNICATION PROTOCOL
• Always check the LRC checksum of answer data. When the LRC checksum is incorrect, do not
use the data. When incorrect data caused by noise is accepted, parameters might be set with
unexpected values. In this case, the processing of an equipment application may judge that it is a
communication failure. When the LRC checksum is incorrect, receive the answer data again with
the following methods.
- Resend the answer data again from SIM by sending "NAK" within 1500 msec after receiving
the answer data. However, when using RS485, send "NAK" at least 1 msec has passed after
receiving the answer data.
- Stop the communication process once, and try the communication process again.
The answer resending process by NAK sent
when LRC is incorrect value.
Figure 41 - Example of answer resending process
• If the next command is sent before receiving the answer data from the SIM, the contents of the
answer data and the sent command from the SIM will not match.
In this case, stop the communication for approximately 5 seconds to clear all the receiving buffer
of an equipment application, and then start the communication again.
It seems that different answer data from
sending command is responded.
Figure 42 - 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. Crosstalk between sending 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 43 - Example of command sending during answer data reply
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