We've got a number of R1 controllers that are old enough to have serial numbers below 600,000. According to the user guide:
"SNAP-PAC-R1s with serial numbers lower than 600,000, and all SNAP-PAC-R1-Bs, are limited to eight 4-channel digital modules per rack; the remaining eight can be analog, serial, and high-density digital modules."
In the case of the R1-Bs, they mount to a "B series" rack. And a limitation of the B Series racks is that 4-channel digital modules must be mounted on one end of the rack (the first 8 slots).
"Four-channel digital modules can be placed in the first eight positions only; 32-channel digital modules can be placed in any position."
OK. So I understand all of that. But:
If I were to use one of these older (S/N lower than 600,000) R1 controllers on a 12 or 16 place SNAP-PAC-RCK, would I be able to place my eight allowed 4-channel digital modules anywhere on the rack as long as I don't exceed 8 total? Or would I be limited to placing such modules in only the first 8 positions of a SNAP-PAC-RCK due to the limitations of the old R1?
My guess is that the limitation is due to less discrete connections in the bus in the case of the B-Series racks and brains. But perhaps the older R1s also do not bring out these extra connections on their bus connector, so they'd also require the 4-Channel digital modules to be placed in the first eight positions even though the rack itself has the extra lines brought from the second eight positions to the controller's bus connector.
I'll be able to figure this out for myself soon enough when I have some spare racks and brains in my hands to play with, but I thought this might be something someone can verify for me ahead of time.
Currently, all of these old R1s are on 8 slot racks, so this issue was moot. But we'd like to know if we can use these old R1s as spare controllers for existing 16-position racks without needing to juggle the positions of the modules and, of course, move the field wiring to accommodate them. For the most part, we don't have more than eight four-channel digital modules in these racks, but since there were no position restrictions, the various modules were installed so as to make the wiring more logical and "tidy", or just added as the systems evolved over time.