Pete Keillor wrote:

I much preferred tags. Having to use a physical address everywhere in
the programming kept me from adopting plc's for quite a while. The
mapping of tag to physical address happens at tag definition usually,
although not always. I had occasion to use a fair bit of repetive
programming, lots of similar pumps, etc. Tags made it easy. Just
copy, paste, change the physical address. I did a fair bit of control
stuff, but it wasn't my main job. Now that I'm retired, I don't
expect I'll be doing that again.

Oh, I never used physical addresses except back when I was using a hand held programmer
for a SLC 100 or 150 and some other ancient thing.

As soon as I was using PC based programming software, I used symbolic addressing so I:1/2
was refered to as UP_PB (up push button). Much easier to program that way. To a degree
with good symbols the code tended to be self documenting.

I've run into machines where the original ladder files with all the nice comments and such
couldn't be found. I end up plugging in, grabbing a current processor image and then
determine what various buttons, switches and coils do and start using symbols to name them
in the ladder so I can form a mental picture of what is going on.

Wes