TriContinent C24000, Product Manual

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CAN interface communications
C-Series Product Manual
113
CAN interface communications
CAN (Controller Area Network) is a two-wire, serial communication bus.
It eliminates polling sequences that verify task completion. Using CAN,
the pumps asynchronously report to the master host when they have fin-
ished the current task.
Note: The pumps use a CAN controller chip compatible with Philips Semi-
conductor CAN bus specification, version 2.0. This is also compatible with the
CANOpen standard.
CAN messages
Standard CAN messages consist of 18-bit frames. Each frame has a 12-bit
arbitration field and a 6-bit control field. These are all the bits that must be
considered at the programming level. On the physical CAN hardware
there are additional bits that occur in a message, such as the start bit
and CRC Field bits; but these are not discussed here, since they are
implemented at the hardware level.
Within the arbitration field, there is an 11-bit message identifier (MID),
and within the control field a 4-bit data length identifier.
The eleven MID bits are used to:
• Indicate which device on the bus the message involves.
• Identify the message type.
• Show the direction of the message (either to or from the master device).
The 4-bit data length identifier within the control field represents the
length of the data block.
Data blocks can be from zero to eight bytes in length. Any message that
requires more than eight bytes must be sent in a series of multi-frame
messages. The receiving unit then assembles the data in the separate
frames into one long string.
CAN message construction
The CAN messages format used to communicate between a host and
the pump are described in this section.
Each message frame begins with the message identifier (MID). The CAN
data block (up to 8 bytes in length) follows the MID and length informa-
tion. The MID makes up three nibbles that are transmitted first in a mes-
sage frame. The bits are grouped as shown below:
CAN arbitration field CAN control field
CAN
data
block
MID RTR IDE r0 Data
Length
(DLC)
Direction Group Device Frame
X 010 XXXX XXX 0 0 0 XXXX 0-8
Bytes