Mitsubishi MELSEC LJ71C24, User Manual

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6 SETTING AND WIRING
(2) RS-422/485 interface operation
1) RS-422-485 interface structure
The following illustration shows the structure of the C24 RS-422/485 interface
driver (send)/receiver (receive).
Receive data
Send data
SDA
SDB
RDA
RDB
Output control input ( 1)
Receiver
Driver
1 "Output control input" (also called send gate) of
the driver (send) section of the illustration at
the left determines whether or not data from
SDA/SDB is output to the outside.
2) RS-422/485 interface operation
When the "Output control input" in the illustration above is ON, the interface
enters the low impedance state (state in which data can be sent).
When the "Output control input" is OFF, the interface enters the high
impedance state (state in which data cannot be sent).
3) Timing to start sending and to complete the transmission processing of the
C24
• Timing to start sending
During data transmission, the C24 outputs the actual data after sending a
mark of 2 characters or longer, after the high impedance set by the
operations described in 1) and 2) is reset.
• Transmission processing completion timing
The following times are necessary as H/W gate OFF time from the time that
data transmission is completed until transmission processing is completed
(the state changes to the high impedance state). (The transmission rate set
in the C24 is the object.)
When the transmission rate is 600 bps or higher : Data transfer time of
less than 1 bit.
When the transmission rate is 50 bps, 300 bps : several ms