1747-SN Remote I/O M-File "mapping"?

[sharkster411 0]

Hello, I'm working with some old Allen-Bradley SLC5/04 systems with 1747-SN modules. The module is located in Slot1. One system is only using the RIO module for a PV1000. How do you know where the "M-Files" for Analog I/O modules and/or Panelviews are located? I see programming using locations such as: M1:1.810 where 60 words are being copied from a Remote I/O PV1000 to some words for the SLC to utilize, but I don't understand why "M1:1.810" was used instead of, for example, "M1:1.800"? I looked and so far cannot find information pertaining to the words other than what is in the User's manual, and it doesn't address this issue. The panelview in my example uses all of Logical Rack 0, Full Rack addressing. Any help would be most appreciated. I have very little experience with the RIO stuff because almost everything I've worked with in the past has been Devicenet.

[Ken Roach 194]

The "M file" data is located in the module itself, and it takes about a millisecond for the SLC to retrieve it from the module every time you reference it. That's why programmers typically use COP instructions to move data blocks in and out in bulk. The M-files are used for module and network diagnostics, and also for moving Block Transfer data into and out of the module. You'll see that the M-file size is typically 3300 words. That's because there are 32 block transfer buffers of 64 words each, but to make addressing simpler for us ten-fingered monkeys, the designers reserved blocks of 100 words for each buffer. As to why your specific programmers used element 10 instead of element 0 of the block transfer... hard to say. I recommend checking out the PanelView's tag database to see how they've assigned digital and analog tags to the Block Transfers they are using. The addressing is not going to look obvious because we're gluing together different technologies from the 70's and 80's; RIO was built for the PLC-2/3/5 but added onto the SLC and the PanelView.