Edwards STP-iS2207 Series - 5.3.12 Application Note

STP-iS2207 Series Turbomolecular Pump
MT-89E-001-C
Page 87
5
SERIAL COMMUNICATION PROTOCOL
5.3.12 Application note
Noise generated by many factors such as the type or length of cable, communication speed, and
different communication devices may cause the communication failure with a serial port. It is very
difficult to prevent a communication failure completely. The followings are the methods to create the
tool application with redundancy to a noise etc.
Be sure to communicate according to the protocol. If it communicates by a different method from
the procedure described by this manual, communication failure might cause.
Figure 43 shows the block diagram of the valid communication process from command sending to
answer data receiving.
Moreover, the example of a communication procedure is shown in Figure 47, Figure 48, and
Figure 49.
PC
SIM
ACK
Reply (A)
Answer
Reply (A)
Command
Send (A)
ACK
Send (A)
Command
Send (B)
ACK
Reply (B)
Answer
Reply (B)
ACK
Send (B)
Figure 43 - Block diagram of communication process example
The SIM will reply "ACK" or "NAK" within approximately 2 seconds after receiving command.
When there is no reply, the SIM may not have received the command. In this case, resend the
command from the tool application before recognizing the process of the communication failure. If
the problem cannot solve after resending several times, make the process of the communication
failure on tool application.
SIM discards the data being received when 5 seconds elapsed without completing the command
from the command receive start.
Send a command from tool application again.
A finishing of data received process should monitor with received character "Etx".
Receiving process is completed by receiving the "LRC" (checksum) data after getting "Etx".
This process can reduce the task of modifying the tool application when commands with different
answer data size according to the pump model are received.
However, when the completion of the answer receiving process is determined by the number of
received characters, check that "Etx" has been received and LRC checksum is correct.
After sending the command, release the elapsed time process due to communication timeout
each time when receiving answer data. When a large number of answer data is received, the
answer receiving process of the tool application is timed out, and all data may not be able to
obtain.