Edwards SCU-801

SCU-801 Control Unit for Turbomolecular Pump
MT-95E-001-A
Page 70
5
SERIAL COMMUNICATION PROTOCOL
5.3 Protocol specifications
5.3.1 General description
The STP serial communication protocol enables the SIM to receive the communication command
(Figure 44, item 1), transmitted from the PC and send a response (Figure 44, item 2), following the
communication command. Each communication command from the PC transmits a text message
(ASCII text) assigned to each function. Communication commands include control commands (STP
pump operation commands, and so forth) and query commands (read-out of STP pump operation
mode, and so forth).
1. Communication command
2. Response
Figure 44 - PC to SIM communication
Table 19 shows ASCII characters being used in the transmission control, error control and handshake
in the application layer. Note that the transmission frame form differs depending upon the
RS232/RS485 single point connection and RS485 multi-point connection. (refer to Section 5.3.8)
ASCII
character
HEX
code
Function
Transmission layer
Stx
02
Transmission block start character
Etx
03
Transmission frame end character
Etb
17
Transmission block end character
Ack
06
Acknowledgment response
Nak
15
Non-acknowledgment response
@
40
Network frame ID character
Application layer
#
23
Acknowledgment response
!
21
Non-acknowledgment response
Table 19 - Transmission control characters