RuggedCom RuggedRouter RX1100 - Manual (Page 218)

24. Configuring Serial Protocols
Revision 1.14.3 218 RX1000/RX1100™
• Packetize on full packet.
If configured to packetize on a specific character, the server will examine each received character
and will packetize and forward upon receiving the specific character. The character is usually a <CR>
or an <LF> character but may be any ASCII character.
If configured to packetize on a timeout, the server will wait for a configurable time after receiving a
character before packetizing and forwarding. If another character arrives during the waiting interval,
the timer is restarted. This method allows characters transmitted as part of an entire message to be
forwarded to network in a single packet, when the timer expires after receiving the very last character of
the message. This is usually the only packetizer selected when supporting ModBus communications.
Finally, the server will always packetize and forward on a full packet, i.e. when the number of
characters fills its communications buffer (1024 bytes).
24.1.3.4. Use of Turnaround Delays
Some RTU protocols (such as ModBus) use the concept of a turnaround delay. When the host sends
a message (such as a broadcast) that does not invoke an RTU response, it waits a turnaround delay
time. This delay ensures that the RTU has time to process the broadcast message before it has to
receive the next poll.
When polling is performed, network delays may cause the broadcast and next poll to arrive at the
remote server at the same time. Configuring a turnaround delay will enforce a minimum separation
time between each message sent out the port. Note that turnaround delays do not need to be
configured at the host computer side and may be disabled there.
24.1.4. TcpModBus Server Application
The TcpModbus Server application is used to transport Modbus requests and responses across IP
networks.
The source of the polls is a Modbus “master”, a host computer that issues the polls over a serial line.
A TcpModbus Client application, such as that implemented by the RuggedServer accepts Modbus
polls on a serial line from a master and determines the address of the corresponding RTU. The
client then encapsulates the message in TCP and forwards the frame to a Server Gateway or native
TcpModbus RTU. Returning responses are stripped of their TCP headers and issued to the master.
The TcpModbus Server application accepts TCP encapsulated modbus messages from Client
Gateways and native masters. After removing the TCP headers the messages are issued to the RTU.
Responses are TCP encapsulated and returned to the originator.
A “native” TcpModbus master is one that can encapsulate the Modbus polls in TCP and directly issue
them to the network.
24.1.4.1. Local Routing At The Server Gateway
The Server Gateway supports up to 32 RTUs on any of its four ports. When a request for a specific
RTU arrives the server will route it to the correct port.