4-6
888-2473-001
2/25/03
WARNING: Disconnect primary power prior to servicing.
Section 4 Theory of Operation
ATLAS Series™
4.3.3
Controller Area Network (CAN) Bus
The Controller Area Network or CAN bus is a high speed serial communications
link which is used between the transmitter control boards for transmission of
control, status, fault and metering information.
The CAN bus is distributed as
part of the System Control Bus (ribbon cable)
. The CAN bus can operate at
speeds up to 1Mbps and is designed to operate in hostile industrial environments.
The transceivers feature cross wire, loss of ground, over voltage and over
temperature protections. A CAN transceiver connected to the CAN bus is
considered a Node. There can be up to 110 nodes on the bus with a maximum bus
length of about 40 meters for 1Mbps operation.
In a CAN system, data is transmitted and received using Message Frames. Message
Frames carry data from a transmitting node to one or more receiving nodes. The
messages transmitted from any node on a CAN bus do not contain addresses of
either the transmitting node or of any intended receiving node.
Instead, the
content
of each Message Frame (e.g. ON, OFF, PS 1 Voltage, Coolant
Flow OK etc.) is labeled by an identifier that is unique throughout the network. All
other nodes on the network receive the message and each performs an acceptance
test on the identifier to determine if the message, and thus its content, is relevant to
that particular node. If the message is relevant, it will be processed; otherwise it is
ignored.
The micro modules have a built in CAN controller which connects to a CAN
Transceiver which becomes a node on the CAN bus. The CAN transceiver
interfaces the single ended CAN controller to the differential CAN bus for high
common mode noise immunity, as shown in Figure 4-2. All of the control boards
can send and receive information over the differential CAN bus, however the Main
Controller determines what information is sent and when it is sent for this
application.
NOTE:
There is an LED on the Main Controller, DS24, which will flicker on and off
at a random rate indicating that there is activity on the CAN bus. If the LED is
off or always on, then the CAN bus is most likely not communicating.
Figure 4-2 CAN Transceiver Diagram
1
8
7
6
5
4
3
2
Standby
Control
Reference
Voltage
Transmitter
Receiver
VREF
RXD
TXD
RS
CANH
CANL
GND
VCC
TXD and RXD
connect to the
CAN controller
built into the
Micro Module
(Differential CAN Bus)
Summary of Contents for Atlas DVL400
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