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Legacy PLC Manual

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I started a new job here in South Jersey. The plant is using a 1747L-40A PLC. They don't have the program or any information regarding this unit. They want me to replace it with a ML. Is there any source for manuals or communication protocol for this old guy?

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Wow, never even hear of this one before.  I looked it up on AB's literature website and found a manual, please see attached.

Appears to be a fixed IO version of a SLC.  Probably a forerunner to the eventual ML series.  It has 24 Digital Inputs @115 VAC and 16 Relay Digital Outputs.  You could add a 2-Slot expansion rack and add additional IO.  Just for giggles, I opened up RSLogix500 (v8.40.00 CPR 9) and started a new project and found the L40A as a valid controller type.

1747-um009_-en-p.pdf

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1747-L40A is one of the old "fixed SLC" controllers, the very first of the "Small Logic Controller" family.   They were introduced in 1988 or so.

They have one of A-B's oldest (but very popular) operating systems.    Networking is via the proprietary Data Highway 485 (DH485) protocol only;  that's not an Ethernet jack (and has +24 volts on it) so don't plug it into an Ethernet switch or port.

Fortunately it's well supported by RSLogix 500 software;  you don't have to resurrect a DOS box with AI-500 or APS.

Unfortunately DH485 is very hard to do with modern computers and serial ports.   The usual way to communicate with these is with a 1747-UIC purpose-built USB to DH485 interface device.

The program should translate easily to a MicroLogix family controller;  they use very similar operating systems and instruction sets.   The conversion process just involves selecting a different CPU type in RSLogix 500.

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Thanks to both of you for such a quick response. I didn't think I would ever find that manual. Thanks to pcmccartney1 for the link!!

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