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― Hardware: The RTS and CTS lines are used when hardware flow control is enabled in both the Fusion and the
remote device. Fusion puts RTS in a mark condition to tell the remote device that it is ready and able to receive
data. If Fusion is not able to receive data (typically because its receive buffer is almost full), it will put RTS in the
space condition as a signal to the remote device to stop sending data. When Fusion is ready to receive more
data (that is, after data has been removed from its receive buffer), it will place RTS back in the mark condition.
The complement of the RTS wire is CTS, which stands for Clear To Send. The remote device puts CTS in a mark
condition to tell Fusion that it is ready to receive the data. Likewise, if the remote device is unable to receive
data, it will place CTS in the space condition. Together, these two lines make up what is called RTS/CTS or
hardware flow control. Fusion supports this type of flow control.
― None: The RTS line is always in a mark condition (always on) and the CTS line is ignored by the Fusion.
Note: Software flow control (XON/XOFF) is not available on the Fusion.
DSR and DTR handshake
DTR stands for Data Terminal Ready. DSR (Data Set Ready) is the companion to DTR in the same way that CTS is to
RTS. Some serial devices use DTR and DSR as signals to simply confirm that a device is connected and is turned on.
Fusion can set DTR to the mark state (i.e. ON) when the serial port is opened and leaves it in that state until the port
is closed. Conversely, Fusion can monitor the DSR line to assess the presence and readiness of the remote device.
― DSR Input: Supported values are Ignored or Connect to remote when on.
If set to Ignored, no action is performed by the Fusion.
If set to Connect to remote when on:
- In TCP client mode, the Fusion will attempt to connect to the remote.
- In TCP server, it starts the service and waits for remote connection.
- In UDP, it starts the service, opens the socket, and is ready for data transfer.
― DTR Output: Supported values are Always off, Always On, or On when connected to remote.
If set to Always off, Fusion puts the line in space condition (that is, off) and leaves it there.
If set to Always on, Fusion puts the line in mark condition (that is, on) and leaves it there.
If set to On when connected to remote:
- In TCP client or server mode, Fusion sets the line to mark when connected to a remote.
- In UDP mode, the state is always connected and therefore the line is always set to mark.
Inter-Character Timeout
Indicates when a packet received from the serial port is to be considered complete. When the time between two
successive characters is greater than this value, the packet is considered complete and sent to the remote.
Supported values are 100 ms, 200 ms, 300ms, 400 ms, or 500 ms.
Note: Packets received from the serial port are also limited in size to 255 bytes (by the Linux kernel). This means that a
packet received from the serial port is considered complete and is immediately sent to the remote as soon as 255
consecutive bytes are received from the serial port. This may have an impact of time-sensitive protocols that make use
of packets larger than 255 bytes.
Fusion Multi-Network LTE Router PN 001-0000-602 Rev. B
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