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Figure 48 Multi-host Function Demonstration
As shown in figure 48, in common mode, when the two hosts: host A and host B connect
the serial device server at the same time, host A send (1) instruction, RS485 device
received (2) instruction, RS485 device return (3) instruction, but at the Ethernet port of
the serial device server it will send (4) to host A and (5) to host B at the same time.
Because host B didn
’t sent query but receives the reply order (5), it may cause
communication error. In multi-host mode, there only have the instruction (4) without (5),
as the serial device server will automatically remember the host required return, only
return the instruction to the recent communication host, as host A query only return to A,
host B query only return to host B.
The other effect is that in normal mode the data sent by host A and host B at the same
time will do instruction combination at the RS485 bus, thus unable to identify properly;
The serial device server can dispatch A and B to use the sequence of the bus, so as to
effectively solve the conflict problem of multi-host simultaneous access.
7.5 Multi-host Parameter
"RS485 Multi-host Support" and "RS485 Bus Collision Detection Function" are
introduced as follows.
Figure 49 RS485 Multi-host Support
The maximum wait time of RS485 query command is: the maximum time interval of the
serial device server serial port sending the command to receiving the reply. The filling
time should be greater than the actual maximum time interval. Because if identified to
timed out, it will send the next instruction.