
5 Serial Gateway
5-28
CJ-series Serial Communications Units Operation Manual for NJ-series CPU Unit(W494)
It is possible to send Modbus-ASCII commands to access Modbus-ASCII Slave devices that are con-
nected to a PLC via a serial network (Modbus-ASCII).
•
Sent message: command code 2805 hex + Modbus-ASCII command
•
Message after conversion: Modbus-ASCII command
z
Sending Messages Using SendCmd Instructions in CPU Unit's User Program
The Unit converts the messages to Modbus-ASCII protocol for this operation.
Note 1
The header contains the following information.
•
Remote destination network address (DNA): Network address to specify actual remote
Pocasset 0 (local network).
•
Remote destination node address (DA1): Node address to specify actual remote Pocas-
set 0 (communications within local PLC).
•
Remote unit address (DA2):
Unit address of serial communications port. An appropriate value is calculated and set
as follows:
When port 1 is used: Unit address = BYTE#16#80 + BYTE#16#04
×
Unit number (hexa-
decimal)
When port 2 is used: Unit address = BYTE#16#81 + BYTE#16#04
×
Unit number (hexa-
decimal)
2
The contents of the Modbus-ASCII command enclosed in the message that is sent is as
follows:
Slave address (ASCII) + FUNCTION code (ASCII) + Communications data (ASCII)
The header ":" (3A hex) and LRC+CR/LF are not required when sending commands. They
are added automatically for serial communications.
5-4-5
Converting to Modbus-ASCII
System Configuration
CPU Bus-to-Serial
Details
From the CPU Unit on the same controller, it is
possible to access the Modbus-ASCII Slave-com-
patible devices that are connected to the Serial
Communications Unit via a serial network (Mod-
bus-ASCII).
2805
message
Header
Modbus-ASCII command
(Via network or CPU bus)
Modbus-ASCII command
Modbus-ASCII command
(RS-232C or RS-422A/485)
CPU Unit
(SendCmd
instruction)
Modbus-ASCII command encapsulated using
command 2805 hex
Serial Com-
munications
Unit
Modbus-
ASCII Slave-
compatible
device
2805
Header
SendCmd
Modbus-ASCII command
Modbus-ASCII command
Serial Communications Unit
Message
RS-485 (Modbus-ASCII)
CPU Unit
Protocol
conversion
Modbus-ASCII
Slave device
Содержание CJ1W-SCU22
Страница 192: ...4 Using Protocol Macros 4 56 CJ series Serial Communications Units Operation Manual for NJ series CPU Unit W494...
Страница 250: ...6 No protocol Mode 6 22 CJ series Serial Communications Units Operation Manual for NJ series CPU Unit W494...
Страница 460: ...A Standard System Protocol R 126 CJ series Serial Communications Units Operation Manual for NJ series CPU Unit W494...
Страница 473: ...Index 1 CJ series Serial Communications Units Operation Manual for NJ series CPU Unit W494 I Index...