9.
Serial communication
Following serial protocols are supported:
Gamma Protocol
9.1.
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 3. 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
See table below for more detail on packet structure.
Field
Size
Comment
1
START
1 ASCII character
ASCII character is ‘~’ (TILDA)
ASCII representation of the tilde ‘~’ character. 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
The command code must be two hex digits, even if the first is a zero. See
for list of available command codes.
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 an X and a Y value, the command field could be followed by two
data fields (X and Y) separated by a comma. All data must be sent in ASCII printable
format (no binary or “control” characters).
5
CHECKSUM
2 ASCII hex characters
Computed checksum of
packet
The calculated checksum must have its value in ASCII hexadecimal notation. It is
calculated by adding the decimal value of all characters in the packet (excluding
start, checksum, and terminator), and then dividing the result by 256. The integer
remainder converted to two ASCII hex digits is the checksum. When a remote
device receives a packet, the passed checksum is compared with a computed
checksum and if they do not match, the device discards the packet.
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900035_B - Serial communication
