N Data file

[robert804 0]

How many different ways to fill in i.e. n20:0. Most of the time it is in the ladder or coming from the HMI. I have seen a register and know little on what puts the data inside. I know there is data cause I see the next move from n:20 out. I have data coming in on port 0 from an input device that reads it through an ARL block shiftd into a string r.

[Bill Linne 0]

Robert: The data can come from many places. It really depends upon what else is connected to the PLC. In my system, we use radio telemetry to gather data from many distant sites. Each site has a block of memory to which it writes. Then that data is displayed on the HMI. (Obviously, the same is true for the HMI to control the distant stations.) Also, other PLC's around the plant can MSG (message) data to each other, so certain areas of memory are reserved for that activity. They are interconnected via DH+ and Ethernet. Analog input modules will also write into whichever area they are configured to do so. Many possibilites. You'll need to track it down. Bill

[Ken Moore 23]

Bill is right, there are several possible sources. What type of PLC are we talking about? Are there other plc's on some type of network with this one?

[Firetubes 1]

...indirect addressing is another way.