UDTs, Structured Text & IO Aliasing

[ohnedich6]

Hello All,

Figured I would join the forum after looking for some information on the web and under the search function of this site. I figured i would join to try and get the communities thoughts/opinions/knowledge with what I'm trying to determine is an acceptable way to program:

I have created a UDT in ControlLogix 5000 Rev. 20 that i have named Pump.
Pump contains the following pieces of data:
Auto -> BOOL
Man -> BOOL
Fault -> BOOL
Ready -> BOOL
Running -> BOOL
Speed -> REAL

I have created a tag (Controller or Program, atm i'm just testing things out) called PMP_1 which is a data type Pump. The BOOL data types in the UDT of Pump are actual hardwired inputs to a DI card (1734-IB8 for this program) that i will need to reference, and the REAL is an AI card (1734-IE8C).

What i'm trying to figure out is if it is a good practice to "alias" the parameters of PMP_1 using structured test in the following way:

PMP_1.Auto := AENTR:1:I.0;
PMP_1.Man := AENTR:1:I.1;
ETC...

Or should i just created program tags and alias them the normal way?
PMP_1_Auto alias to AENTR:1:I.0
PMP_1_Man alias to AENTR:1:I.1
ETC...

If this has been discussed i apologizes and could someone point me in the right direction. Thank you for your help.

Regards,
Nathan

 

[Phrog30]

Hello All,
Or should i just created program tags and alias them the normal way?
PMP_1_Auto alias to AENTR:1:I.0
PMP_1_Man alias to AENTR:1:I.1
ETC...

The software will not allow you to alias the "normal way". You will need to map the IO to the members, like you described using ST.

One thing to note, which you seemed to do, is to keep the data types contiguous, expecially BOOL. If you were to move one of the BOOL after the REAL, you will notice that it will take another 4 bytes of memory.

My two pennies.

James

 

[ohnedich6]

James,

Thanks for that. I wasn't 100% sure if mapping the IO via ST is a common practice or if it's something that should be avoided all together.

On a side note, would it be beneficial to have a TIMER in my Pump UDT as let's say a minimum run timer or should i just keep that as a tag outside of the UDT?

-Nathan

 

[Phrog30]

James,

Thanks for that. I wasn't 100% sure if mapping the IO via ST is a common practice or if it's something that should be avoided all together.

On a side note, would it be beneficial to have a TIMER in my Pump UDT as let's say a minimum run timer or should i just keep that as a tag outside of the UDT?

-Nathan

I would add in the UDT, if it were me.

For me, I would map using ladder, not ST. That's just because most of my customers are not well schooled in ST and would hate me for it. But, that's your call.

James