Edwards SCU-800 - Transmission Frame in the RS485 Multi-Point Connection

SCU-800 Control Unit for Turbomolecular Pump
MT-49E-101-G
Page 72
5
SERIAL COMMUNICATION
PROTOCOL
5.3.8 Transmission frame in the RS485 multi-point connection
To identify a network frame and ensure the compatibility with a standard transmission frame, add a
network frame ID character "@" and a title of 3 characters of network frame number to the
transmission frame in the RS485 multi-point connection.
The network frame number is specified by any 16 bits signed hexadecimal value coded ASCII text of 1
to 127, to identify the SIM.
Examples: Network frame ID character and number in the multi-point connection
ASCII
@
0
1
Network frame No "1"
HEX
40
30
31
ASCII
@
6
4
Network frame No "100"
HEX
40
36
34
ASCII
@
7
F
Network frame No "127"
HEX
40
37
46
The transmission frame has a single block or multiple transmission blocks. Each transmission block
consists of a network frame ID character, a network frame number, a start control character, data
block number (3 digits), a message (up to 255 characters), an end control character and a checksum
(LRC). The following shows the transmission frame when the message transmission character string
is C
n
.
Transmission frame when a message is below 255 characters (n<=255):
1
2
3
4
5
6
7
8
8+n
8+n+1
8+n+2
ASCII
@
F
1
F
2
Stx
0
0
1
C
1
C
n
Etx
LRC
"@" is used as a network frame ID character.
"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
6
7
8
8+n
8+n+1
8+n+2
Block
ASCII
@
F
1
F
2
Stx
0
0
1
C1
1
C1
n
Etb
LRC
Second
1
2
3
4
5
6
7
8
8+n
8+n+1
8+n+2
Block
ASCII
@
F
1
F
2
Stx
0
0
2
C2
1
C2
n
Etb
LRC
Final
1
2
3
4
5
6
7
8
8+m
8+m+1
8+m+2
Block
ASCII
@
F
1
F
2
Stx
k
Ck
1
Ck
m
Etx
LRC