Re: [foxboro] Integrator 30 Modbus Connection to Multilins

I've had some experience with Modbus gateways and whilst I am certainly not
an expert I can suggest the steps that I follow when configuring these
devices. One point though, if you can talk with a PC successfully but not
the Multilin device then this suggests to me that your RS232 hardware
handshake lines may set incorrectly - for the gateway to communicate,
hardware handshaking must actually work or configured so that the gateway
thinks it's working - or you need to swap the TXD/RXD lines. 

So moving right along . . .
1.      Set the P0970VB as for 3-wire configuration as per figure 2-26 in
B0193RL. This is a 'null-modem' configuration that configures the hardware
handshake so that the gateway will always transmit and receive. 
2.      Configure the ECBPG as required and if all is well then SysMon
should display this as white in System Management. 
3.      You should not go beyond this point until the ECBPG shows continuous
white.
4.      Configure the ECB16 as required but disable the heartbeat option
unless you are sure your device handles this function code.
5.      Configure the MDSCAN, MCIN etc blocks as required. I generally
configure a reduced set until the communication issues are sorted out.
6.      I then connect a laptop with Modbus emulation software (ModbusView
from Ocean Controls is rather neat) to the RS232 DB25M connector on the
P0970VB. 
7.      Since the gateway is always a master you should observe message
packets being transmitted from the gateway and by entering data into
appropriate registers via the emulation software, message packets should be
sent back to the gateway and be observable on the DCS.
8.      You should not go beyond this point until the ECB16 shows continuous
white with the correct data being received.
9.      Next disconnect the PC and connect the RS232/RS485 device. This will
involve a slight reconfiguration of the P0970VB since the communications
will change from [DTE (Gateway) - DTE (PC)] to [DTE (Gateway) - DCE
(Converter)]. Open SW1-1, SW1-2 and close SW3-1, SW4-3. This connects TXD of
the gateway to TXD of the converter and RXD of the gateway to RXD of the
converter.
10.     Most converters will work like this - without actual DTE-DCE
hardware handshaking - but some may actually require hardware handshaking
particularly if 2-wire RS485 is used rather then 4-wire RS485 since the line
needs to be 'turned-around' from transmit to receive and visa versa.
11.     If you need actual hardware handshaking for the converter to operate
okay, then try the next steps in order
12.     Configure the P0970VB: Open SW1-7, SW1-8 and close SW3-2, 3-3. This
enables CTS/RTS handshaking.
13.     Configure the P0970VB: Open SW2-2, SW3-5 and close SW1-4, SW2-6.
This enables DTR/DSR handshaking.
14.     Configure the P0970VB: Open SW3-2, SW3-3 and close SW1-7, SW1-8.
This disables CTS/RTS handshaking but leaves DTR/DSR handshaking active.
15.     You will need to set up the 3rd-party device end (Multilin) to
communicate appropriately for the RS485 link.
16.     After communications are established with the 3rd-party device with
the reduced data set, then configure the remainder.

Be aware that some RS232-RS485 converters may not work correctly with the
gateway when using 2-wire RS485 as the line turn-around takes time and if
the converter does not take this into account with its hardware handshake to
the gateway, then the gateway will start sending data too early causing
problems. (Example: don't use Westermo converters with gateways in a 2-wire
RS482 system).

Hope this helps a little.
Regards
Paul Augustine
Foxboro - Karachaganak Unit 3


        -----Original Message-----
        From:   Landriault, Yvon [mailto:YLandriault@xxxxxxxx]
        Sent:   Saturday, May 24, 2003 12:28 AM
        To:     'foxboro@xxxxxxxxxxxxx'
        Subject:        [foxboro] Integrator 30 Modbus Connection to
Multilins


        To all:

        We have a Foxboro Integrator 30 for Modbus Controllers and I would
like to
        connect that up to a Modbus compliant device which speaks rs485
Modbus RTU.


        The configuration is basically the Int30, an RS232/485 converter and
the
        Modbus device (Multilin).  The device settings are 2400,8,N,1 (half
duplex).

        We have tried in vain to make this work.  The ECB block to go
on-line.  We
        can use a PC and talk to the Modbus device however.  When we try to
put the
        ECB16 block online it times out.  The RS232/485 converter flashes
(ie: the
        232 sends out a signal).

        We also tried to use an ECB20 block however we got an "Invalid
Block"
        message when we tried to save it.

        Has anyone out there set up a similar configuration.  If so, could
you
        please forward some details including cabling configuration, dip
switch
        setting (P0970VB) and the ECB block configuration.  

        Thanks in advance.

        Yvon..

        Yvon Landriault
        Senior CA&E Engineer

         
         
        
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