Software Communication 3-13
Device
This is the address of the module in the particular group. Each group can have up
to 16 devices. The address value is 0 - 15.
Frames
This lets the device know what type message is coming. See “CAN Frame Types.”
RTR
This bit is not used in Cavro’s CAN implementation and should always be set to 0.
Length
This is the length of the data block in the message. Data blocks can be from zero to
eight bytes in length.
CAN FRAME TYPES
The frame types allow each device to know what type of command is coming in and
enables faster processing of commands. Pumps respond to the frame types described
below.
“On-the-Fly” Commands (V and T)
Normal commands use a frame type 0 of “1” (i.e., “Action Commands”). Since
commands sent over the CAN bus with a particular frame type must complete
before a subsequent command using the same frame type can be issued, a different
ID must be used when issuing an “on-the-fly” command. For this reason, “on-the-
fly” moves must be issued over the CAN bus with a frame type of “0” (zero). Note
that a frame type of “0” specifies Set commands.
When issuing “on-the-fly” commands, the “frame type 0” commands will not
generate completion messages and thus no pairing code is needed (these commands
are simply acknowledged immediately).
Action Frames, Type 1
This frame type is used for action commands, such as Initialization commands,
Movement commands, Valve commands, or to set pump operating parameters. All
“task-type” commands are sent in this type message frame. When multi-frame
messages are used to send an action command, this frame is the end message sent
to the pump.
Common Commands, Type 2
This frame is used for commands that are common to every device on the bus. The
frame type is set to 2 and the command is a single ASCII character in the data
block. The single ASCII character is described below.
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