Internet PLC Forum

sounds like the conveyor won't run as long as the pack sensor detects a box.  Using relays, allow the pack sensor to stop the conveyor only one time per box.  (clear the relay when the sensor is false again)  I prefer latching relays for this.

Switch selector position B with  Start button pressed should open a N.C. relay that keeps the pack sensor from stopping the belt.

In a real world situation you would want to implement a timer in such fashion that clearing the above mentioned relay would only occur if the sensor was false for a specified amount of time.  This would keep the sensor from cycling due to irregularities in the box, conveyor, etc...

If this dosen't help.... http://users.adelphia.net/~s1ick/jpeg001.jpg
Don't look if you don't need to.  It's just a logic puzzle.

I'm currently working on a project using the M-7024 and M-7018.  The most versatile method I've found for doing what you are attempting, is to use a RS232 to RS485 adapter with the PLC and the Input module(s) all on the same twisted pair.  You can plug your computer into the adapter and communicate with either the PLC or with the 7018.  You will not be able to communicate with them simultaneously.  Either TL server or the DCON utility must be running, not both.  I left the converter inside the cabinet for ease of troubleshooting in the future.  This also leaves the RS232 port of the PLC open for future growth, ie... HMI, Internet, Printer....
Also, you will get lot's of errors using DCON(master) if the PLC(master) is trying to communicate with the I-7018.  There are numerous ways to overcome this problem.
A simple DPST toggle switch can be used to isolate the PLC from the rest of the network while you are using DCON.  Power off the PLC.  Activate an input that will halt PLC communication.... many ways.  Activating an input is probably the cleanest method.
Hope this helps.

Dogface

Just use a NPN prox switch with a toothed gear.  Or if it is a high speed application, use a HESS (Hall Effect Speed Sensor)  Unless rotary encoders have come down in price dramaticaly, this solution is both economical and simple.

I tried removing the "Start In:" information.  NOT a good thing.  The program couldn't find the help files.

Yes....checked the firmware version.  It is r49.  Like I posted previously.  I'm not sure why the Setsystem command didn't work.  I just know that it didn't.

I don't want to seem negative towards the PLC.  This thing is great!  Not to say it is perfect, but what a powerfull tool!

thanks,
Sean

This is my communication with ICP-DAS regarding some of the issues I've had with the M-7018 input module.  If you have the time and inclination to go through it, please correct me if my information is faulty or misleading.
Thanks.  ;)

Hi John,
I'll do my best to relay the information correctly....
Using a "M" series Tri-Plc and the M7017 input module.

The Tri-Plc manual shows using the following TBasic command to read the inputs on the M-7017
READMB2 ch, ID, addr, var, count      {* Applicable only to M+PLC with firmware r44 or higher}

Example:  
readmb2 13,3,0,DM[10],8   *ch 3 is for ASCII, and ch13 is for RTU.

I had no luck with this command.  Communication Error reported between the PLC and the Module.  I believe that the problem is....this command implements a Modbus RTU function 03x (read holding register) which is not supported by the M-7017.  A Modbus RTU function 04x (read input register) is required.

Tech-Support recommended that I precede the above mentioned command with "setsystem 5,4" to force the PLC into using the function 04x instead of the 03x.  This did not work.  I don't know why...it just didn't.

Looking further, I found a sub-routine that was written by Tri-Plc's tech support guru.
'  This function implements MODBUS RTU function 04 using the INCOMM and
'  OUTCOMM commands.
'  The address to be read is in A
'  The number of channel to be read is in N
'  The data are returned in DM[201] to DM[201+N]
'  DM[101] to DM[200] are used by this function
DM[101] = &H02     ' node address of slave
DM[102] = &H04     ' function 04
DM[103] = A/256    ' upper 8 bit of address
DM[104] = A & &HFF ' lower 8 bit of address
DM[105] = 0        ' upper 8 bit of count
DM[106] = N        ' lower 8 bit of count
X = CRC16 (DM[101],6) & &HFFFF  ' compute the CRC16 of DM[101] to DM[106]
DM[107] = X / 256    ' upper 8 bit of CRC16
DM[108] = X & &HFF ' lower 8 bit of CRC16
FOR I = 1 to 8          ' send out the MODBUS RTU command in binary
  OUTCOMM 3, DM[100+I]
NEXT
delay (10)  ' delay for a while to wait for response
FOR I = 1 to 90          ' assuming small number of read data
  DM[110+I] = INCOMM (3)
  IF DM[110+I] < 0 GOTO @5: ENDIF
NEXT
@5 FOR I = 1 to N          ' convert two bytes into one 16-bit word.
  DM[200+I] = DM[112+I*2]*256+DM[113+I*2]
NEXT

I had some limited success with this snipet of code and further modified it as follows...

dm[101]=&h02  'address of module
dm[102]=&h04  'modbus protocol code to read modicon input register
dm[103]=&h00  'Start address high
dm[104]=&h00  'start address low
dm[105]=&h00  'Read 8 channel high
dm[106]=&h07  'Read 8 channel low
X = CRC16 (DM[101],6) & &HFFFF  ' compute the CRC16 of DM[101] to DM[106]
DM[107] = X / 256    ' upper 8 bit of CRC16
DM[108] = X & &HFF ' lower 8 bit of CRC16
FOR I = 1 to 8          ' send out the MODBUS RTU command in binary
  OUTCOMM 3, DM[100+I]
NEXT
delay (10)  ' delay for a while to wait for response
FOR I = 1 to 30          ' assuming small number of read data
  DM[110+I] = INCOMM (3)
  IF DM[110+I] < 0 GOTO @5: ENDIF
NEXT
@5 FOR I = 1 to 16          ' convert two bytes into one 16-bit word.
  DM[200+I] = DM[112+I*2]*256+DM[113+I*2]
NEXT

almost identical.

It's working, but it was a painfull chore to make it work.  Having said that....I'm just a rookie.

Thanks,
Sean

Okay.  Herein lies the problem...I think.  The M-7018 uses the Modbus function 0x04 to read the input registers.  The standard should be 0x03, but it isn't.

I'm using a T100MDr49 but using the command setsystem 5,4 doesn't help the issue.  Is this command valid for both ASCII and RTU?

I downloaded and used http://www.tri-plc.com/trilogi/modbusFunction04.zip with somewhat limited success.  Actually, it may have been completely succesfull.  I just can't decipher the information returned in dm(200)- ? .

Any suggestions?

Thanks,
Dogface