It's a common question that clients ask, “Which MicroLogix's support Modbus?” In this article I'll detail the answer.
Today’s MicroLogix 1000 still has just one Mini-Din RS-232 “Channel 0” communication port limited to DF1 and DH-485. So for applications requiring Modbus you'll need to look elsewhere, as the MicroLogix 1000 does not support Modbus.
Series C versions of the MicroLogix 1200's Mini-Din RS-232 “Channel 0” communications port supports DF1, DH-485, ASCII, MODBUS RTU SLAVE and MODBUS RTU MASTER. However, the series A and B models only support MODBUS RTU SLAVE.
Since “Channel 0” is limited to RS-232, to put the ML1200 on RS-485 I recommend the 1761-NET-AIC which is an isolated RS-232 to RS-485 interface converter. You’ll also want the 1761-CBL-HM02 cable to connect and power the AIC.
Series C versions of the MicroLogix 1500's Mini-Din RS-232 “Channel 0” communications port supports DF1, DH-485, ASCII , and MODBUS RTU SLAVE and MODBUS RTU MASTER. The LRP models also support DF1, DH-485, ASCII , MODBUS RTU SLAVE and MODBUS RTU MASTER on its DB9 RS-232 communications port labeled “Channel 1.” While series A versions of the LSP model has no MODBUS support, series B versions of the LSP and LRP do support MODBUS RTU SLAVE.
Since “Channel 0” (and “Channel 1” on LRP models) is limited to RS-232, to put the ML1500 on RS-485 I recommend the 1761-NET-AIC. For “Channel 0″’s Mini-Din connection you’ll also want the 1761-CBL-HM02 cable to connect and power the AIC. For “Channel 1″’s DB9 connection you’ll need either a 1761-CBL-AC00 (17.7”) or 1747-CP3 (9.8′) (you’ll also need to provide 24vdc power to the AIC.)
On the ML1100, Rockwell re-designed “Channel 0” removing the Mini-Din pins that previously provided 24vdc to accessories (like the AIC) and replaced them with RS-485 connections. So, to put the ML1100 on RS-485 you can use the Mini-Din to Terminal Block cable, the 1763-NC01.
Like the ML1100, the ML1400’s “Channel 0” port has RS-485 connections in place of the 24vdc power pins, so to put the ML1400's “Channel 0” on RS-485 you would use the Mini-Din to Terminal Block cable, the 1763-NC01.
To connect the ML1400 DB9 RS-232 “Channel 2″ communications port to RS-485 I recommend the 1761-NET-AIC with a 1761-CBL-AC00 (17.7”) or 1747-CP3 (9.8′) (and don’t forget you’ll also need to provide 24vdc power to the AIC.)
Unique to the series B versions of the MicroLogix 1400 is the added support for MODBUS TCP on the “Channel 1” Ethernet port. The port is the standard RJ-45 style and supports 10 MBPS Half Duplex through 100 MBPS Full Duplex.
I hope the above information on which models of MicroLogix support Modbus was helpful. Later in the week I’ll cover which CompactLogix and ControlLogix models support Modbus. Until then, if you have any comments or questions please feel free to leave them by filling out the “post a comment or question” link below.
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