DirectSoft 6 - Modbus

ThomasGruetter

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Join Date
Jan 2010
Location
Florida
Posts
63
PLC model D0-06DD2-D: I uploaded the program from a defective unit and installed it in a new PLC.
Com port 2 is used for modbus communication to 2 drives. The communication to the drives on the new PLC does not seem to work. The port was setup properly under PLC/Setup/Setup Sec. Comm. Port... with same parameters as on the old unit.
Is there something I missed ? I also up/downloaded v-memory data.
Note this is my first time using DirectSoft.
 
Tried that and switched PLC's several times to see if I missed something.
The port setup is okay and don't think that port is defective out of the box.
So I missed something else?
 
What was the problem with the PLC you replaced? Was the drive communications working with the original PLC?
 
The old PLC has welded output relays.
The code is using SP116 and a 1 second time bit (SP4) as conditions to send the drive command (speed).
The condition is NOT SP116 and SP4 then modbus command.
The SP116 seems to be in on state and the signal command never gets excecuted?
As I don't understand what SP116 is I might just remove it and see if it works.

Modbus.png
 
The SP116 bit is true when the port is busy. There is also a SP117 bit which is defined as "Port error". You should check that.
I'm not fond of your logic. SP4 is on for 500 mS and off for 500 mS. There is a better example in the DL06 manual on page 4-28. You need to take steps to make sure you only process one MRX or MWX per program scan.
 
Last edited:
That is the part I don't understand. What is SP116? It is used 4 times and the condition seems always off - therefore command is not sent. The second drive is using the time bit on condition. Forgot to attach earlier. I guess trying to avoid collision of commands?

Modbus_2.png
 
SP116 and SP117 are special relays in the DirectLOGIC CPUs that monitor the PLC’s communications. SP116 is on when Port 2 is communicating with another device
 
I found using Stage logic best for sequential communication commands. One command per stage. In each stage just wait for the busy bit (SP116 in this example) to be off then trigger the MWX/MRX command then JMP to the next stage. The last stage JMPs to the first.
 

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