Channel configuration for ML1400 PLC

MicroLogix 1400 User Manual said:

The MicroLogix 1400 controllers provide three communications ports, an isolated combination RS-232/485 communication port (Channel 0), an Ethernet port (Channel 1) and a non-isolated RS-232 communication port (Channel 2). The Channel 0 and Channel 2 ports on the MicroLogix 1400 can be connected to the following:

• operator interfaces, personal computers, etc. using DF1 Full Duplex point-to-point
• a DH-485 network
• a DF1 Radio Modem network
• a DF1 half-duplex network as an RTU Master or RTU Slave
• a Modbus network as an RTU Master or RTU Slave
• an ASCII network
• a DeviceNet network as a slave or peer using a DeviceNet Interface
(catalog number 1761-NET-DNI)
• an Ethernet network using the Ethernet Interface module
(catalog number 1761-NET-ENI, or 1761-NET-ENIW)
• a DNP3 network as a Slave

When connecting to RS-485 network using DH-485, DF1 Half-Duplex Master/Slave, Modbus RTU Master/Slave or DNP3 Slave protocols, the MicroLogix 1400 can be connected directly via Channel 0 without an Advanced Interface Converter, catalog number 1761-NET-AIC. The Channel 0 combo port provides both RS-232 and RS-485 isolated connections. The appropriate electrical interface is selected through your choice of communication cable. The existing MicroLogix 1761 communication cables provide an interface to the RS-232 drivers. The 1763-NC01 cable provides an interface to the RS-485 drivers.

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shailesh_vb said:

Hello everyone,

I have doubt regarding ports of Micrologix 1400 PLC.

Channel 0 and Channel 2...

Channel 0 is Rs232C or RS485 or can be configured as both?

Correct. By selecting your protocol and using the correct cable the Channel 0 port will be auto configured as either an RS-232 or RS-485 electrical interface. You can connect directly, using only a cable, as this port is electrically isolated from the device or network you are connecting to.

Same for Channel 2.

Not correct. Channel 2 uses an RS-232 only port. You can select the same communication protocols as Channel 0, except that where a protocol uses an RS-485 electrical interface, such as MODBUS, you must use an RS-232 to RS-485 converter, such as a 1761-NET-AIC. Also, because Channel 2 uses a non-isolated port, when using RS-232 communication protocols, it is best practice to use the 1761-NET-AIC as an optical isolator between RS-232 devices.

Because I did Modbus RTU Slave on Channel 0 and checked it with Modscan software. And used no RS485 to RS232 converter in between PLC and PC.

You know it works, but now you know a little bit more about why it works.

Thanks,
Shailesh.

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