GridConnect CAN USB-232, Руководство пользователя

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Getting Started
CAN USB-232 User Manual 2-31
2.7.11 Set CAN Command Mode Message Output Termination
2.8 CAN Virtual Command Mode
In virtual circuit mode, the CAN USB-232 establishes a full-duplex, virtual circuit between itself and
another CAN USB-232 or application device. By providing a virtual circuit over the CAN network,
applications can exchange serial stream data in a network-transparent fashion, using existing CAN network
cabling as a data link (Figure 4).
Figure 4
The CAN USB-232 takes data bytes coming into the serial port and groups them into CAN messages for
transmission. When a remote CAN USB-232 or application target receives these messages, it extracts the
data bytes and recreates the original data stream on its serial output port. This operation is fully transparent
to the connected application devices.
The virtual circuit requires two, user-configurable, CAN identifiers in order to identify the source &
destination devices for the circuit. Since virtually every CAN protocol provides a sub-set of unused or ‘user-
specific’ identifiers, establishing a virtual circuit on a CAN network in conjunction with an existing protocol
is supported and very easy to do.
The CAN USB-232 only sends CAN messages when eight bytes of data have been received. This leads to a
case where the last part of a data stream is not sent if it is less than eight bytes long. To deal with this in a
transparent fashion, the CAN USB-232 provides a timeout feature that will automatically force a
transmission of the last accumulated byte(s) after a specified maximum waiting time.