Edwards SCU-1601

SCU-1601 Control Unit for Turbomolecular Pump
MT-96E-1B1-0
Page 87
5
SERIAL COMMUNICATION PROTOCOL
ASCII
Stx
0
0
1
#
Etx
LRC
HEX
02
30
30
31
23
03
EC
However, when the MSB (most significant bit) is always 0 when data length is 7 bits, LRC is set to
6C
hex
.
5.3.7 Error control
• Transmit the transmission frame repeatedly from the PC when the SIM transmits “Nak” (parity
check error). When the SIM receives “Nak” from the PC, the transmission frame is transmitted
again. This operation is repeated up to 5 times.
• The SIM transmits “Ack” or “Nak” to the PC after the completion of communication command
reception. When the PC cannot receive “Ack” or “NaK” after 2 second, retransmit the
transmission frame from the PC.
When these communication status occur repeatedly, display to an error message or start the error
routine on the PC.
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):