3 - Software Communication
Communication Protocols
Cavro® XLP 6000 Modular Syringe Pump Operating Manual, 734237-C, en
3 - 5
The following two scenarios clarify this error detection mechanism.
Scenario 1.
1
The computer sends a command block stamped with sequence #1 to the
pump.
2
The pump receives the command, sends an acknowledgement to the PC, and
executes it.
3
Transmission of the acknowledgement message is imperfect; the PC does not
receive it.
4
The PC waits 100 ms for the acknowledgement, then retransmits the
command block with the sequence number left at 1 and the repeat bit set to
indicate a retransmission.
5
The pump receives the transmission, identified as such by the repeat bit.
6
The pump checks the sequence number against that of the previously
received command block. Noting a match, the pump sends an
acknowledgement to the PC, but it does not execute the command (since it
has already been executed).
7
The PC receives the acknowledgement and continues with normal
communications.
8
The next command block is stamped with sequence #2 to indicate a new
command.
Scenario 2.
1
The computer sends a command block stamped with sequence #1 to the
pump.
2
The pump never receives the command due to a communication error and
thus does not send an acknowledgement to the PC.
3
The PC waits 100 ms for the acknowledgement, then retransmits the
command block with the sequence number left at 1 and the repeat bit set to
indicate a retransmission.
4
The pump receives the retransmission, identified as such by the repeat bit.
5
The pump checks the sequence number against that of the previously
received command block. Noting a mismatch, the pump recognizes this as a
new command block and sends an acknowledgement to the PC. It then
executes the command.
6
The PC receives the acknowledgement and continues with normal
communications.
7
The next command block is stamped with sequence #2 to indicate a new
command.
The sequence number/repeat byte is constructed as follows:
Bit #
7
6
5
4
3
2
1
0
Value
0
0
1
1
REP
SQ2
SQ1
SQ0
