Frame Control (Checksum); Error Control; Transmission Frame In The Rs485 Multi-Point Connection - Edwards STP-iS1607 Series Instruction Manual

5.3.6

Frame control (checksum)

5
The transmission frame is controlled by the odd number parity check. First initialize LRC as FF
Next calculate LRC by EXCLUSIVE-OR (XOR) of all the frame bytes containing "Stx", "Etb", "Etx"
and LRC and transmit the result as LRC.
Examples:
Character string for calculation before calculating LRC.
ASCII Stx
HEX 02
Calculation of LRC:
02 XOR 30
hex hex
Character string for transmission after calculating LRC.
ASCII Stx
HEX 02
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.
MT-94E-001-C
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STP-iS1607 Series Turbomolecular Pump
0 0 1 #
30 30 31 23
XOR 30 XOR 31 XOR 23
hex hex
0 0 1 #
30 30 31 23
Etx LRC
03 FF
XOR 03 XOR FF
hex hex
Etx LRC
03 EC
hex
= EC
hex hex
.