Help with DF1 Protocol command to retrieve N7 integer values from Micrologix 1200 PLC

Hello everybody. I am currently trying to retrieve the Integer data file values from a micrologix 1200 via VB6. I have constructed a string that is being sent out the com1 port of my PC to the PLC, but believe I have something incorrect with the string as the value returned are not the value in the N7 data file. As you are aware AB is real helpful in documenting this, and I can't afford RSLinx Pro to retrieve the values thru DDE/OPC. Any help with this would be appreciated. Below is the string I am using to retrieve data:

com$ = Chr(16) + Chr(2) 'Start DF1 message
com$ = com$ + Chr(1) + Chr(0) 'destination / source node addr
com$ = com$ + Chr(1) + Chr(0) 'command / status
com$ = com$ + Chr(transnbr%) 'transaction number
com$ = com$ + Chr(0) + Chr(0) 'address
com$ = com$ + Chr(0) + Chr(2) 'size
com$ = com$ + Chr(16) + Chr(3) 'End DF1 message

followed by the BCC for this string

The PLC responds with the DLE/ACK and then returns the data to me, but as I said it isn't the value of N7:0 when viewed with RSLogix500.

Again, any help with this would be appreciated.

Just a wild guess!

Try swapping the bytes

Thanks for the input...

Gerry,

Thanks for the input, I've tried swapping the bytes around but still am not getting the data from N7:0

I really need the hex character sequence of the unprotected read for source Node 0 to destination Node 1 with the address sequence,etc to be sure I am reading the DF1 protocol manual correctly for the 1200.

The 1200 is not in the Allen-Bradley documentation (although I believe that it is like the micrologix 1000 and slc5xx series).

I've been searching the web for days looking for a monitor mode example without success.

Thanks again for the suggestion... I appreciate all inputs as this problem is driving me nuts... (LOL)

I hate assumumptions but...

I have written a driver for a MicroLogix 1500 and SLC. Both the SLC and the Micrologix 1500 worked the same. I looked at what you are doing and it looks right to me. It may be that the Micrologix 1200 works more like a SLC than a MicroLogix 1000. In this case the data you recieved was in N:9 not N:7 as in the MicroLogix 1000. This CIF is N:9 on the SLC.

Try the SLC typed read and write. That is what we use on the SLCs and Micrologix 1500.

Note, I never would have responded unless you made it clear that you have read the DF1 manual and did not find info on the 1200. I was surprise that I couldn't find info on the MicroLogix 1200 either. I now I am as curious as you. Let us know if the MicroLogix 1200 is more like a 1000 or a SLC.

RSDoran, I don't respond to posts because I hate guessing, making assumptions and asking 20 questions. In this case there may be no other option because there isn't DF1 info on the Micrologix 1200.

Thanks for the insight...

Peter,

Thanks for the insight, I hadn't thought of the CIF file being N9 instead of N7... I'll give that deeper research. Thanks for the reply, I really appreciate it, this little snag is costing me lots of valuable time in developing my HMI. When this is solved everything will be "downhill" from there.

Thanks again, I'll check on this and let everybody know what I found.

Bingo!!

Peter,

Thanks a million!!! That was the answer... The Micrologix 1200 CIF file is N9 NOT N7... like in the 1000 (even though the 1200 uses N7 as its Integer Data File by default! I really appreciate that... maybe next time it'll be my turn to help you out...

Have a GREAT day!

Thanks Again!

David,

Peter is correct. The N9 is the CIF for the Micrologix 1200. Also be sure that your code is able to handle sending and receiving a 10 hex(DLE) in either the upper or lower byte of your data block. You need to include an extra 10 hex(DLE) when transmitting and you need to filter out the extra 10 hex(DLE) when receiving.

Thanks for the info

ROBO,

Thanks for the info on the DLEs. I appreciate the reminder about them and will handle them accordingly.