Mitsubishi MELSEC LJ71C24, Руководство пользователя

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6 SETTING AND WIRING
6.3.5 Enabling or disabling echo back of the RS-422/485 interface
The following describes the enabling and disabling of the echo back.
This function can be used for CH2 of the LJ71C24.
The echo back of the LJ71C24 is defined as the function that, when data are sent
through RS-485 (2-wire type) from the RS-422/485 interface, the same data are also
sent to RDA or RDB of the LJ71C24.
Whether to receive the returned data or not (discard) can be specified.
SDA
SDB
RDA
RDB
LJ71C24
SDA
SDB
RDA
RDB
Sending data
Target device
Receives or not receive
(discards) the data.
(1) Application
1) Disabling the echo back will eliminate the processing for ignoring
unnecessary data, which has been programmed for nonprocedural protocol
communication.
2) When the same message format is used for request (command) and
response in the predefined protocol communication, proper communication
with the other device can be performed by disabling the echo back.
(2) Setting method
1) Setting by GX Works2
Configure the setting in the following item.
"Various_Control_Specification" screen "For designation of communication
control" "Echo back allow/prohibit designation (for RS-422/485 I/F)"
For details, refer to Section 7.2.
2) Setting by the sequence program
Store either of the following values in the echo back enable/disable setting
area (address: 450(1C2
H
)). (Default: 0)
Setting value Description
0: Enable echo back
When the LJ71C24 sends data, it also receives the
sent data in its own RDA or RDB.
1: Disable echo back
When the LJ71C24 sends data, it does not receive the
sent data in its own RDA or RDB. (The data are
discarded.)