29
The PicoLAS Protocol
The following section describes the structure and possible commands of the PicoLAS protocol.
Structure
Structure
Structure
Structure
Each transmission consists of 12 bytes – called a frame as follows – which must be sent consecutively.
Otherwise the system times out and the transmission must start again from the beginning.
A frame has a fixed structure. The first two bytes describe the command, the following eight bytes the
parameters, followed by one reserved byte and one checksum byte. The checksum is calculated out of
the first 11 bytes which are linked by a bitwise XOR.
Thus a frame has the following structure:
Byte
Meaning
1
Bit 8-15 of the command
2
Bit 0-7 of the command
3
Bit 56-63 of the parameter
4
Bit 48-55 of the parameter
5
Bit 40-47 of the parameter
6
Bit 32-39 of the parameter
7
Bit 24-31 of the parameter
8
Bit 16-23 of the parameter
9
Bit 8-15 of the parameter
10
Bit 0-7 of the parameter
11
Reserved, always 0x00
12
Checksum
A properly received frame must be acknowledged by the recipient with an answer, which is also a
frame. If the acknowledgement does not occur the command has not been processed and the
sending procedure should be repeated.
If the recipient recognizes the command as valid, but not the parameters, then it will answer with an
ILGLPARAM (0xFF12) as command.
In case that the recipient receives an invalid command it will answer with UNCOM (0xFF13).
If a faulty checksum is recognized then the answer is RXERROR (0xFF10). If this error occurs often the
connection should be checked.
Using the REPEAT (0xFF11) command the recipient can instruct the sender to send the most recent
frame again.
