So I am working on projects that have been on PLC5s for years now. One of our goals is to eventually migrate to ControlLogix, however in the meantime we are still using PLC5s in the short-term and, of course, when existing systems need maintenance. Everything is validated, so any major changes to a PLC, much less an entire line of PLCs, take forever (you should see the paperwork to change XIC to XIO!).
Anyways, over the years they began to run out of space on the PLC5s, so eventually they resorted to a very modular and generic form of code to impliment, but however it uses massive indirect addressing (5+ levels in some places). As the code grew, it became more and more messy (though I have to say they did a good job with what they had).
The main goal of all this indrect addressing was to save space, however at the cost of code readability. And it has gotten me thinking...
Is indrect addressing really THAT much more effective in saving memory space? Even if it is, it seems to me that the cost, in terms of the time it takes for an engineer, especially new ones coming in, to learn or re-learn a piece of code, seems too great to warrant the massive amounts of indirect addressing required to save memory.
As I am relatively new to automation compared to the many of you out there, I was just curious on the general consensus on indrect addressing and its advantages/disadvantages.
With something like ControlLogix, at least any indirect addressing can be done using tags and structures. With what I have seen with PLC5, it can be much more confusing and overwhelming.
Anyways, over the years they began to run out of space on the PLC5s, so eventually they resorted to a very modular and generic form of code to impliment, but however it uses massive indirect addressing (5+ levels in some places). As the code grew, it became more and more messy (though I have to say they did a good job with what they had).
The main goal of all this indrect addressing was to save space, however at the cost of code readability. And it has gotten me thinking...
Is indrect addressing really THAT much more effective in saving memory space? Even if it is, it seems to me that the cost, in terms of the time it takes for an engineer, especially new ones coming in, to learn or re-learn a piece of code, seems too great to warrant the massive amounts of indirect addressing required to save memory.
As I am relatively new to automation compared to the many of you out there, I was just curious on the general consensus on indrect addressing and its advantages/disadvantages.
With something like ControlLogix, at least any indirect addressing can be done using tags and structures. With what I have seen with PLC5, it can be much more confusing and overwhelming.
.)
