Edwards SCU-1600

SCU-1600 Control Unit for Turbomolecular Pump
March 10 70 Issue 1-a
5
SERIAL COMMUNICATION PROTOCOL
Table 20 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
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
Transmission layer
@ 40 Network frame ID character
# 23 Acknowledgment response Application layer
! 21 Non-acknowledgment response
Table 20 - Transmission control characters
5.3.2 Standard transmission frame (in the RS232/RS485 single point connection)
The transmission frame used in the RS232/RS485 single point connection has a single block or
multiple transmission blocks. The transmission block consists of a start control character, data block
No. (3 digits), a message (up to 255 characters), an end control character and a checksum
(Longitudinal Redundancy Check (LRC)). The following table shows the transmission frame where the
message transmission character string is C
n
.
Transmission frame when a message is below 255 characters (n<=255):
1 2 3 4 5
5+n 5+n+1 5+n+2
ASCII Stx 0 0 1 C
1
C
n
Etx LRC
"Stx" and "Etx" are used as a start and an end character of the transmission frame, respectively.