PLC2 Conversion - Addressing Question

[ctleng76]

I am working on a conversion project to upgrade a machine's controller from a PLC2 to a CompactLogix. I know how the inputs and ouputs are addressed, however there are some output coils addressed as 030/0X and 031/0X. This would seem to indicate there is a rack 3, however there is only one physical rack. Is this an internal memory address? Other than that there are a bunch of 04X and 05X timer addresses.

Thanks in advance!

 

[GaryS]

Depending on the rack configuration there may be a rack 3 its just not obvious. you have to check the dip switches on the racks refer to the manual.

are you planning on reusing the old racks of replacing them you can use them with the CompactLogix
Either way the I/O addressing is different and will have to be adjusted to what you are using

Just a side note Rockwell at one time had a service where they would convert PLC2 programs to PLC5 (for a fee)
then the migration from PLC5 to Logics is much easier you may want check with then to see if its still available

 

[dmargineau]

I am working on a conversion project to upgrade a machine's controller from a PLC2 to a CompactLogix. I know how the inputs and ouputs are addressed, however there are some output coils addressed as 030/0X and 031/0X. This would seem to indicate there is a rack 3, however there is only one physical rack. Is this an internal memory address? Other than that there are a bunch of 04X and 05X timer addresses.

Thanks in advance!

Just remember that the old PLC platforms (2,3 and 5) are using the Logical Rack concept; a Logical Rack refers to a memory location partition and not a physical rack (chassis).
Modern controllers automatically map any application component device data within memory partitions carrying the respective device identifiers.
It looks like your PLC2 has at least 5 "active" Logical Racks (PLC2s support a maximum of 7 Input and 7 Output Logical Racks).

http://literature.rockwellautomation.com/idc/groups/literature/documents/pm/1772-pm003_-en-e.pdf

The new CompactLogix will need to contain at least the same number of Inputs and Outputs as the PLC2 used; while the PLC2 could support 896 Inputs and 896 Outputs the functional count is probably less than that; you will have to identify them though and start adding...

 

[James Mcquade]

ctleng76,

Its been a while, so here goes.

The plc 2 series allowed you to use the output addresses of plc racks as internal outputs (this was from my plc 2 teacher)
and they may not be actually there.

Timers and counters used 2 addresses located 100 words apart from memory). More than likely, the t04x is the preset and timer 05x is the address for the enabled, timer timing, done bit, and so on.

you may want go google plc2 instruction manuals.

hope this helps,
james

 

[TConnolly]

ctleng76,
The plc 2 series allowed you to use the output addresses of plc racks as internal outputs (this was from my plc 2 teacher)
and they may not be actually there.

This.

The PLC/2 had fixed input and output image tables, with an input word and an output word for every logical rack/slot up to the limit of the PLC IO. It was possible to use all of those addresses, even when there was no physical IO present. Even though it is not the best programming form, many programmers would go ahead and use them as internal bits. As you've just discovered, years down the road this bad practice causes headaches because now you have to determine if there really was IO there or not.

 

[James Mcquade]

TConnolly,

thanks for the additional information.
james

 

[jdbrandt]

I am working on a conversion project to upgrade a machine's controller from a PLC2 to a CompactLogix. I know how the inputs and ouputs are addressed, however there are some output coils addressed as 030/0X and 031/0X. This would seem to indicate there is a rack 3, however there is only one physical rack. Is this an internal memory address? Other than that there are a bunch of 04X and 05X timer addresses.

Thanks in advance!

All the other responders are correct. Non-physical data table addresses can be used for programming, timers, etc. Totally legal, and, back-in-the-day, usually needed because of the small amount of memory.
However, with the information given, we can draw no conclusions.
JUST BECAUSE 04x and 05x are timers does NOT mean that there's not a rack 6 or higher actually in use.
DIP switches are the rule of the day on this, expecially with remote racks.
And, the BIT level addressing in a PLC-2 is, as you may know, OCTAL (no 8's, no 9's.
In your 030/ and 031/ reference, the '0' means output, the '3' means logical rack 3, the "0" or "1" means Module Group, and, the 0X would be the bit.

 

[Mike_RH]

"JUST BECAUSE 04x and 05x are timers does NOT mean that there's not a rack 6 or higher actually in use."

I have to disagree with this. It has been 30 years, but with a PLC-2 you defined the size of the IO image table, and then the size of the data table.
So if you had a two rack system, the outputs would be 010 to 027 (words), the inputs would be at 110 to 127 (words). The addresses are in octal. After the IO image tables would come the timer & counter addresses.
So using a two rack system, 030 would be the first timer / counter address for the accumulator. The presets would be 100 higher (octal) at 130.

 

[JaxGTO]

If there are several GET PUT as the first rung with address 030 it is communications to other PLC2's. That's about all I remember from those days.
AB Had a program that would convert PLC2 to PLC5, talk to an older PLC specialist and they may still have a copy. I had one but it was on a floppy that got ruined in a flood.

 

[jdbrandt]

"JUST BECAUSE 04x and 05x are timers does NOT mean that there's not a rack 6 or higher actually in use."

I have to disagree with this. It has been 30 years, but with a PLC-2 you defined the size of the IO image table, and then the size of the data table.
So if you had a two rack system, the outputs would be 010 to 027 (words), the inputs would be at 110 to 127 (words). The addresses are in octal. After the IO image tables would come the timer & counter addresses.
So using a two rack system, 030 would be the first timer / counter address for the accumulator. The presets would be 100 higher (octal) at 130.

Well, you are probably right. Its been two years since I've seen a PLC-2, 15 years since I touched one, and 20 years since I programmed one. Details get lost, sometimes.
If I had one lying around, I'd test this. I'm not sure my T-3 terminal will even boot up again.