The Controller Area
Network (CAN or CAN-Bus) has been invented for use in
vehicles (cars, trucks) to reduce the complexity of the
cabling systems and to allow the control of different
sensors and devices. Because of its reliability against
noise and transmission errors the CAN-Bus is also used as an
industrial "Fieldbus". Today CAN-Bus is mainly used to
control factory automation for many different controlling
and data acquisition applications.
CAN-Bus is a broadcast bus with differential serial data
transmission, where the bits are
being
send in NRZ coded
frames. The frames consist of an ID to identify the sender
type and up to 8 data bytes is sensed from all CAN-bus
nodes. A CAN network can be configured to work with two
different frame formats: the standard frame format has a
11Bits ID (CAN 2.0A) whereas the extended frame format uses
29Bits ID (CAN 2.0B). CAN-Bus features an automatic
'arbitration free' transmission.
A CAN message that
is transmitted with highest priority will 'win' the
arbitration, and the node transmitting the lower priority
message will sense this and back off and wait.
Using the VScom CAN adapters a PC can be connected to the
CAN Network in a simple manner: over USB, over a serial port
or over Ethernet. All VScom CAN adapters support both CAN
2.0A and CAN 2.0B frame format to fulfil the task of
controlling and monitoring. The PC can in the same time
additionally used to log the data and status of the CAN-bus,
without interfering with the control application.
The USB-CAN adapters are
connected to a PC via USB 2.0 and support data speeds up to
up to 1MBit/s over the CAN Network. Also USB 1.1 with the
Full Speed data rate of 12Mbit/s is sufficient to operate
this device. Therefore even older computers are suitable for
CAN operation.
The drivers for Windows operating systems install a virtual
serial port (Com Port). This COM Port is then used by the
software to transfer data and commands to the CAN-bus.
Hardware-based automatic flow control of the COM Port
ensures the reliable data transmission, i.e. no data losses,
to/from CAN bus.
Also under Linux OS drivers emulate a serial port, with
secure flow control as well.
Because the drivers basically emulate a serial COM port,
the users may use a terminal program for data transmission
and control. The binary data of CAN bus are converted to an
ASCII-format, they are sent in this form. This modus may be
used manually, to simply tests the equipment in the
installation phase. Also dedicated customer applications can
use the terminal mode. However this is an effort, which is
not necessary to be done. Instead the customer applications
can use the supplied CAN frame library (a DLL in Windows),
which automatically packs the application data and commands
into the CAN bus frame data format for send, receive and
control/status commands. Using the CAN frame library the
user can focus on his real application,
and don't care about the frame data formats. The CAN Frame
library is developed to be compatible with future VScom CAN
products.
The power supply of USB-CAN is provided via
the USB port, which results in minimum cabling. The low
power consumption is an additional advantage.
The SER-CAN adapter is similar with the
USB-CAN adapter, but it is connected directly to a rs232
serial port of any computer. The SER-CAN adapter has the
same specifications concerning CAN bus interface and
operates the drivers in the in the same way as USB-CAN. The
SER-CAN adapter uses the same CAN frame library as interface
for native CAN frame format. The rs232 interface limits the
maximum data speed on the serial port side, but the adapter
can be configured to filter frames based on certain
information, so it only accepts the matching data. This
feature, optionally combined with suitable higher level
protocols, can significantly reduce the required data
throughput. Further the SER-CAN uses RTS/CTS flow control to
guarantee the error free data transmission.
The SER-CAN is powered by an 5V DC external
power adapter. A suitable wall-plug adapter is part of the
packaging.
Both adapters are available
at
a very attractive price.
Deutsche Version