SCU-801 Control Unit for Turbomolecular Pump
SERIAL COMMUNICATION PROTOCOL
"@" is used as a network frame ID character.
"Stx" is a start character of each transmission block, and "Etb" is an end character of the transmission
block of a message of 255 characters.
"Etx" is used as an end character of the final transmission block (end character of the transmission
frame).
5.3.9 Control command in the RS485 multi-point connection
The control command to be used when a pump operation instruction or a setting change instruction is
transmitted to the SIM and is arranged in the order specified below. The top is "Sp" (space character,
HEX code "20") and ASCII characters corresponding to the respective function code and parameter
follow.
CHR: Function code character, C
1
to C
n
: Parameter
Parameter (from C
1
to C
n
) serves as 16 bits signed hexadecimal value coded ASCII text. When a
message (a space character, a function code, and parameter) exceeds 255 characters, input "Sp" and
CHR to the top transmission block only (the first transmission block of the transmission frame). It is not
necessary to input them to the second and succeeding transmission blocks.
The SIM returns the acknowledgment response character "#" when the control command is processed
normally. If not, the SIM returns the non-acknowledgment response character "!" and 3 characters of
the non-acknowledgment code are added to "!".
Transmission frame when data is transmitted to one block (a message is less than 256 characters):
Designate the control command on the PC.
Always assign less than 254 characters (n< 254) to the parameter so that the message is less than 256
characters.
Next, the preceding SIM->PC character is "Ack", the instructed control command is executed and the
SIM returns the following response.
The PC transmits "Ack" or "Nak"; then transmits the next command if necessary.
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