12.
Serial communication
Following serial protocols are supported:
▪
Gamma protocol
▪
Modbus ASCII protocol
▪
Modbus RTU protocol
Note:
Modbus register map is available on Gamma Vacuum website under download
section.
12.1.
Gamma protocol over serial connection
Gamma protocol command packet structure over serial connection
The command packet is made up of at least five fields. The minimum
command packet (single command with no data) is 11 bytes long. No new
commands should be sent to the controller before the response from the
previously sent command has been received.
Table 4. Command packet structure over serial connection
Start
Space Address Space Command Space
Data
Space Checksum Terminator
1 byte 1 byte 2 bytes
1 byte 2 bytes
1 byte variable 1 byte 2 bytes
1 byte
Field
Size
Comment
1
START
1 ASCII character
ASCII character is ‘~’ (TILDA)
Start is the first byte in the command packet and tells remote controllers to start
decoding a message.
2
ADDRESS
2 ASCII hex characters
Range 00 through FF
This field should be filled in with the hexadecimal representation of the integer address
of the controller. The range provides 255 unique addresses. Only 32 devices may reside
on the same serial port due to hardware loading limitations.
Note:
Must be supplied, even when running RS-232.
3
COMMAND
CODE
2 ASCII hex characters
Range 00 through FF
See
on page 43 for list of available command codes. The
command code must be two hex digits, even if the first is a zero.
4
DATA field(s)
As needed
ASCII printable characters only
Data field(s) are for any commands that have a data value. Not all commands require
data field. If command has more than one data value associated with it, such as setting X
and a Y value, the command field could be followed by two data fields (X and Y)
separated by a comma and space between them. All data must be sent in ASCII
printable format (no binary or “control” characters).
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900031_J - Serial communication
