INFICON STM-2XM 2-Channel Rate/Thickness Monitor - Manual (Page 96)

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STM-2XM Operating Manual
5.7 Windows/SMDP Server Implementation
SMDP server on Windows message timeout is typically 150 milliseconds. That is,
after the host sends a command, it waits 150 milliseconds for a reply. If no complete
reply is returned from STM-2XM in that time, the message is considered lost. This
could indicate the following:
 STM-2XM is offline
 The cable is disconnected
 The baud rate is invalid/mismatched
 There is noise corrupting the packet/checksum integrity
After 150 milliseconds have elapsed, the host can try again.
NOTE: Once a valid connection to STM-2XM is made, the command/response
exchange will proceed at the fastest speed, sending a new command as
soon as the prior answer has come back to the host.
If there is a loss of a packet due to noise, software error, or power loss to STM-2XM,
the loss will be detected when a valid reply packet is not returned within the 150
millisecond timeout.
Retries or resending commands can continue to take place until a valid reply is
returned once the 150 millisecond timeout has been reached.