Edwards STP-iS2207 Series - Frame Control (Checksum); Error Control; Transmission Frame in the RS485 Multi-Point Connection

STP-iS2207 Series Turbomolecular Pump
MT-89E-001-C
Page 82
5
SERIAL COMMUNICATION PROTOCOL
5.3.6 Frame control (checksum)
The transmission frame is controlled by the odd number parity check. First initialize LRC as FF
hex
.
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 0 0 1 # Etx LRC
HEX 02 30 30 31 23 03 FF
Calculation of LRC:
02
hex
XOR 30
hex
XOR 30
hex
XOR 31
hex
XOR 23
hex
XOR 03
hex
XOR FF
hex
= EC
hex
Character string for transmission after calculating LRC.
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.