Re: Allen-Bradley PLC question

[Maren Purves via Tech-talk <tech-talk at aps.anl.gov>]

Hi Mark,

we're still using the abdf1 driver that originated from Jeff Hill in 1995 (says the code) and that I recently asked about. I know that the communication goes through the serial line (which in our case is connected to a console switch and Ethernet from thereon). I don't know anything about the PLC hardware (or internal software) off the top of my head.

Maren Purves
Head of Instrument and Telescope Software
East Asian Observatory / JCMT

On Tue, Jan 31, 2023 at 7:30 AM Mark Rivers via Tech-talk <tech-talk at aps.anl.gov> wrote:

Folks,

 

I have two old Allen-Bradley SLC 500 PLCs with the SLC 5/03 processors.  These are communicating with EPICS via the VME 6008-SV1 scanner card, which is connected to a 1747-DCM “Direct Communication Module” in the PLC.  These communicate via the Remote I/O (RIO) protocol.  We are planning to eliminate the VME crates on our beamline, but really hope to avoid spending the $50K or so that it would cost to replace the PLCs.

 

I am therefore looking for another way to communicate from EPICS to the PLCs. I am not aware of any device that replaces the VME 6008-SV1, for example a PCI-E card or an Ethernet adapter device.  Does anyone else know of one?

 

The SLC-5/03 has an RS-232 serial port 0 that normally uses the DF1 protocol.  It is how we program it from a PC, for example.  It also has an RS-485 port 1 that uses the DH-485 protocol.  It does not have an Ethernet connection.

 

The RS-232 port can be configured to use be a Modbus master.  Unfortunately it cannot be configured to be a Modbus slave, which would allow simple connection to EPICS via the Modbus module.  However, I could enhance the Modbus module to add support for acting as a Modbus slave, and the PLC could then connect to the EPICS IOC and send and receive data.

 

Does anyone know of another option, for example with the DH-485 port?

 

Thanks,

Mark