Edwards SCU-1601

SCU-1601 Control Unit for Turbomolecular Pump
MT-96E-1B1-0
Page 83
5
SERIAL COMMUNICATION PROTOCOL
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.
Transmission frame when a message exceeds 255 characters (n = 255, m<=255, k = the number of
transmission blocks):
First
1
2
3
4
5
5+n
5+n+1
5+n+2
Block
ASCII
Stx
0
0
1
C1
1
C1
n
Etb
LRC
Second
1
2
3
4
5
5+n
5+n+1
5+n+2
Block
ASCII
Stx
0
0
2
C2
1
C2
n
Etb
LRC
Final
1
2
3
4
5
5+m
5+m+1
5+m+2
Block
ASCII
Stx
k
Ck
1
Ck
m
Etx
LRC
"Stx" is used as a start character of each transmission block; "Etb" is used as an end character of the
transmission block with a message of 255 characters; "Etx" is used as an end character of the final
transmission block (the end character of the transmission frame).