Modem to modem using AB SLC 500


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We have a customer where we already have an Allen Bradley modem kit installed. We have a PC set up here at our place with a US Robotics modem that periodically dials the AB modem (which is connected to a SLC/504) and, using RS Linx with a DDE topic, we log data to an Excel spreadsheet and then save it. The problem we have is that sometimes when the modem dials in to the SLC we may or may not get good data because a particular machine we are monitoring may not be running. I have been asked if we can have the AB modem dial in to the US Robotics whenever the machine starts up so we can get good data. I found a Technote at the Rockwell knowledgebase that shows the necessary programming required to have a SLC automatically dial out. I haven't yet tried it. Has anyone ever done this?

Jasmin Ouellet

have you ever consider using an Allen-Bradley Modem ? they have a call back functionality.

this mean that upon certain conditions, the MODEM WILL call you ! this would fullfill your need, and has some other advantage: your customer will be the one paying the long distance, and the chipset in those, has a DF1 protocole.

I haven't used the Rockwell tech note approach personally but I have seen it demonstrated by Rockwell and it seems to work extremely well either between two PLCs or between a PLC and SCADA system. We have also done similar things with Control Logix PLCs using ethernet over PSTN. You need a suitable router (we used Allied Telesyn) which will handle PSTN comms and then you trigger the dial up by sending messages to the ethernet port. This is a very difficult mechanism to set up and not entirely reliable so I would only recommend it where you specifically need an Ethernet connection over a PSTN line, typically when it is used as a backup to a Kilostream or other permanent connection.