SLC 500 MSG Instructions

rbepple

Member
R
Join Date
Mar 2011
Location
Richland, WA
Posts
13
Hi,
I have a SLC 5/04 using the Read MSG instruction to get data from a bunch of ML 1200s. Everything works great and fine other than the fact for some reason I cannot read more than 4 elements from the ML 1200. Is there something I am doing wrong?
 
Welcome to the Forum !

Verify the size of the data table you are reading from the MicroLogix 1200 controller. You should be able to get about 110 Words in a single MSG instruction.

Here's a thought: Are you trying to read the Input or the Output data table ? Those are natively 4 words long on a MicroLogix 1100/1200/1400/1500.
 
Thanks for the quick response! I am trying to read an integer file (N7). the N7:0 is a mirror image of I:0, when I:0/0 is true N7:0/0 is true and so forth. N7:1-3 are mirrors of the analog inputs, the problem is I cannot get N7:4 from the ML 1200 to the SLC 500.
 
quick question: can you post your RSS program files? ... (you'll need to ZIP them first - forum rule) ...

don't get yourself in trouble if your company considers these to be proprietary or trade secret information - but troubleshooting is always easier when we can see the programs ...
 
Sorry I work for the government and cannot share program its a big no-no! The IT department prohibits me from uploading images to an online server. But I will post setup info that is in the MSG setup window.
 
This controller
  • Communication Command: 500CPU Read
  • Data table Address: N19:0
  • Size in Elements: 5
  • Channel: 0
Target Device
  • Message Timeout: 10
  • Data Table Address: N19:0
  • Local Node Addr (dec): 19 (octal): 23
  • Local/Remote: Local
There is no special instructions on the Target Device (ML1200)
 
I cannot read more than 4 elements
Click to expand...

What happens when you set up and run the 5 element read? Does the instruction fail and no infomation is read? Is only the first 4 elements read? What exactly happens?

Does the target have a running program (even if nothing more that the I/O copy instructions). Is it in RUN mode?
 
Last edited:
I have 12 different ML 1200 in remote locations communicating back to this one SLC 5/04 and all of them do the same thing, just reads the first 4 elements and not the 5th and up.
 
If you with your PC, while communications are taking place, write to the 5th location on the Master PLC does that value stay unchanged or does the communications possibly overwrite it with an unexpected value (zeroes possibly)?

Is it possible that code in the Master is overwriting the 5th location?
 
Last edited:
Whatever value I enter in N19:4 at the Master PLC (SLC 5/04) stays there and is not overwritten when the MSG instruction completes. An analog signal is attached on the ML1200 side and then a SCP instruction is used and places the info in N19:4.
 
Just for clarity, in your post number 3 you said you are trying to read N7:?? but in post number 7 your configuration is reading N19:??. Is there a move instruction in your ML1200's to move N7:?? to N19:?? ?
 
I have twelve ML 1200 that the SCL 5/04 is reading from and to keep things simple I matched up data tables with node addresses (for the most part). Example, I read N7 from node 7 and place it in N7 on Master PLC, I read N19 from node 19 and place it in N19 on Master PLC and so forth.
 
I can't see a way for the MSG instruction to complete without an error but the data to not be placed in the target.

Remember that SLC-500 data files start at Element Zero, so an SLC Data Table Read from N19, length 5, will return:

N19:0
N19:1
N19:2
N19:3
N19:4

but not N19:5. It certainly looks like you're counting elements correctly.

If you can capture the serial stream we could tell absolutely for certain how many bytes are coming across the wire. I just think somewhere there's a mis-address or an overlap.

I would create a test program with nothing but a single MSG in it and try that out.
 

Similar Topics

S
Error MSg Slc 500
Hi i am having this reoccurring error on a SLC 500 Allen Bradley plc. Rack Data Detected, check slot 17 and sometimes 19 what could be the cause...
Replies
10
Views
3,041
OkiePC
OkiePC
J
SLC 500 PLC DH+ MSG Help...
Can I send messages via DH+ to PLC's that are located on like different nodes. I'm wondering if this is possible because I have a situation where...
Replies
9
Views
3,880
JoseM
J
L
SLC 500 Changing MSG block transfer IP on the fly!
I'd like to change the IP of a MSG instruction on the fly. I've identified the bits that change in the control block when I change the IP in the...
Replies
5
Views
4,713
Ron Beaufort
Ron Beaufort
M
SLC-500 SQO info wont go through mask
I have a program that I've used 100 times. SQO settings: File N7:0, Mask 0FFFFh, Dest B3:1, Control R6:0, Length 8, Pos 2. Length & Position...
2 3 4
Replies
48
Views
952
drbitboy
drbitboy
J
Slc 500 software & Siemens plc question
Everyone, i am in the process of purchasing the Slc 500 version of software to support what we have and i have a question. Several of our...
Replies
9
Views
761
James Mcquade
J
Back
Top Bottom