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How to Connect a Us Robotic External Modem to an Allen Bradley DF1 PLC

Article ID: 9
Last updated: 13 Oct, 2010

Connecting an external modem to a PLC can save a machine builder a ton of time and labor if that one day is required to troubleshoot your machine 1000 miles away. Allen Bradley offers modem kits that can be installed, however if your trying to save some money why not just use a plain old fashion US Robotic External modem?

Configuration requires two steps:

1. Configure your DF1 port on your Micro Logix 1500 LRP or SLC 5/03 port.
2. Configure your US Robotic modem.

If you are using a Micro Logix 1500, make sure you purchase the LRP model. The LRP model gives you an additional DB-9 port on the side of the processor that you can dedicate to your modem.

First lets configure our DF1 port to the following settings. If you are using a Micro Logix 1500 your port channel will most likely be Channel 1 (the side port). If you are using a SLC 5/03 chances are your port will be Channel 0 (the only DB-9 port on the front of the CPU).

Open up RS Logix 500 and click on Channel Configuration. Setup the channel setting like so:

Current communication mode = SYSTEM
System mode driver = DF1 FULL-DUPLEX
User mode driver = ASCII

CH 0 or CH 1 SYSTEM CONFIG
BAUD = 9600
STOP = 1
Duplicate detect = unchecked
Ack time out = 150
SRC DEC ID = 9
Control line = Full-Duplex modem
Parity = none
Error detect = BCC
Nak retries = 3
Enq retries = 3
Embedded responses = Auto-detect

Download your new Channel Configuration using RS Linx.

Now you can setup your modem. Some older US Robotic modem have settable switches in the back of the modem. If your modem has switches, you'll need to set your switches as follows:

Switch Settings for Usable modems
for Allen Bradley SLC 500 PLC

For a USR 56K Sportster External
Dip Switch

1 up
2 up
3 down
4 up
5 up
6 up
7 up
8 down

If your modem does not have switches, then you'll need to program it using it modem "AT" commands. You'll need an AT Modem Cable (thanks to Randy Ayscue of Pureflow, Inc. to help straighten me out) to program the modem. You'll be using the same AT modem cable to connect the US Robotic modem to the PLC when finished. Some retail box US Robotic modems come with a DB-25 and DB-9 AT modem cable. Plug the DB-25 cable into the modem and connect the DB-9 end to your computer. Using Hyper Terminal, we will need to send some AT strings to the modem to "program" it to accept calls, auto answer etc. etc...It doesn't hurt to send these commands to either an older modem or a newer modem with no switches. You can download my hyper terminal session file at the bottom of this article.

Some AT modem cables can be purchased, here is place I've purchased them in the past.

Start Hyper Terminal, and copy and past these AT commands to the modem. Make sure you use the "Paste to Host" option.

AT&F0
ATY0
AT&W0
ATB0&W0
ATS0=1&W0
AT&A1
AT&B0
AT&C1
AT&D2
AT&G0
AT&H0
AT&I0
AT&K0
AT&M1
AT&N6
AT&P0
AT&R1
AT&S0
AT&T5
AT&U0
AT&Y1
AT&W0
AT&W1

*See AT Reference below

Unplug your modem to restart it. Now take the AT modem cable that you used to program your modem and connect the DB-9 end to your PLC channel.

Next you'll need to plug in a phone line and configure RS Linx to dialup your machine. Follow these steps:

Start RS Linx
Click on Configure Driver
Select RS232 DF1 Devices
Click ADD NEW
Rename it to:
AB_MODEM
Set COM port to MODEM port (usually COM1)
Set Device = SLC-CH0/Micro/Panelview
Set Baud Rate = 9600
Set Station Number = 0
Set Parity = NONE
Set Error Checking = BCC
Set Stop Bits = 1
Click check mark:
USE MODEM DIALER
Click on Configure Dialer
Add a phone number in ADDRESS BOOK
enter your phone line number:
HINT: don't forget the "dial out number" and one comma equal a one second delay.
Click OK should DIAL
Also when finished HIGHLIGHT driver
then click on STARTUP
Set Startup to MANUAL

Congratulations! You have just saved your company a service call.

* AT command reference:

 &A0
             When auto-answering, connect as answering modem
 &A1
             When auto-answering, connect as originating mode,
 &C0
             Presence of carrier detect signal is assumed (ROM default. This value is recalled after &F is issued)
 &C1
             Track status of carrier detect signal
 &C2
             Presence of carrier detect signal is assumed until on-line. From that point, track status of signal
 &D0
             Status of DTR signal is ignored. (ROM Default. This value is recalled after &F is issued)
 &D1
             DTR signal is monitored. The modem enters command state after an on-to-off transition of DTR signal. If the connection is intact, the O0
             command returns to the on-line state.
 &D2
             DTR signal is monitored. The modem hangs up and enters command state after an on-to-off transition of DTR signal.
 &D3
             DTR signal is monitored. The modem hangs up and resets after an on-to-off transition of DTR signal.
 &F
             Recall factory configuration
 &G0
             Guard tones not used (Not supported in Netherlands, Norway, Sweden, Switzerland, or the United Kingdom)
 &G2
             1800 Hz Guard tones are used
 &J0
             Configure for RJ-11, RJ-41S, RJ-45S telco jacks
 &J1
             Configure for RJ-12, RJ-13 telco jacks (Not supported in Netherlands, Norway, Sweden, Switzerland, or the United Kingdom)
 &K0
             Local flow control disabled
 &K1
             RTS/CTS local flow control enabled
 &K2
             XON/XOFF local flow control enabled
 &K3
             RTS/CTS local flow control enabled
 &K4
             XON/XOFF local flow control enabled
 &K5
             Transparent XON/XOFF local flow control enabled
 &L0
             Set for dial-up mode
 &L1
             Set modem for conditioned leased line (private speechband circuit) mode
 &On
             Go to the X.25 PAD command state of channel n(n=0-3) from the AT command state. The modem will return to the command state of last
             channel selected, if a parameter for this command is not specified.
 &Q0
             Communicate in asynchronous mode
 &Q1
             Communicate is asynchronous mode 1 - Async-to-Sync
 &Q2
             Communicate in asynchronous mode 2 - Stored Number Dial
 &Q3
             Communicate in asynchronous mode 3 - Voice/Data Switch
 &Q4
             Communicate in asynchronous mode 4 - Hayes AutoSync.
 &Q5
             Communicate in error-control mode
 &Q6
             For interfaces requiring constant speed between the DTE (computer/terminal) and the DCE (modem), communicate in asynchronous mode with
             automatic speed buffering (ASB)
 &R0
             Track CTS according to RTS
 &R1
             Assume CTS (ignore RTS)
 &S0
             Assert DSR signal always
 &S1
             Assert DSR signal before handshake only
 &S2
             After handshake negotiation, assert DSR signal, but before CONNECT XXXXX result code is sent to the DTE
 &T0
             Halt any test in progress
 &T1
             Start local analog loopback
 &T3
             Start local digital loopback
 &T4
             Grant request from remote modem for remote digital loopback
 &T5
             Deny request from remote modem for remote digital loopback
 &T6
             Start remote digital loopback
 &T7
             Start remote digital loopback with self-test
 &T8
             Start local analog loopback with self-test
 &T19
             Find out if RTS and CTS circuits are supported in the DTE cable
 &U0
             Trellis coding enabled (CCITT V.32 9600 bps only)
 &U1
             Trellis coding disabled
 &V
             View active, user profiles, and stored telephone numbers
 &W0
             Write current configuration parameters in memory as profile 0
 &W1
             Write current configuration parameters in memory as profile 1
 &X0
             Derive transmit clock signal from modem's internal oscillator (internal clock signal on pin 15)
 &X1
             Derive transmit clock signal from attached computer (external clock signal on pin 24)
 &X2
             Derive transmit clock signal from receive carrier (slave receive clock signal on pin 15)
 &Y0
             Set stored user profile 0 as power-up configuration
 &Y1
             Set stored user profile 1 as power-up configuration
 &Zn=x
             Store phone number x in location n (n=0-3)

A - Answer
Function
Command to execute answer sequence.  Modem goes off hook, waits for billing delay time, then sends answer tone and goes into handshake sequence.
Command Syntax
ATA


Command Syntax
AT&C[<value>] <value> = 0 or 1.
Arguments
<value> Decimal number corresponding to the selected option.
0 RLSD is always ON.
1 RLSD follows the state of the carrier. (Default.)


Command Syntax
AT&D[<value>] <value> = 0 - 2.
Arguments
<value> Decimal number corresponding to the selected option.
0 Modem ignores DTR.
1 Upon an on-to-off transition of DTR, the modem enters online command state and issues an OK result code; the call remains connected.
2 Upon an on-to-off transition of DTR, the modem instructs the underlying modem to perform an orderly cleardown of the call. The disposition of any data in the modem pending transmission to the remote modem is controlled by the +ETBM parameter; otherwise, this data is sent before the call is cleared, unless the remote modem clears the call first (in which case pending data is discarded). The modem disconnects from the line. Automatic answer is disabled while DTR remains off.

Command Syntax
AT&K[<value>]
Arguments
<value> Decimal number corresponding to the selected option.
0 Disables flow control.
3 Enables RTS/CTS flow control. (Default for data modem modes.)
4 Enables XON/XOFF flow control.
5 Included for compatibility only and has no effect other than returning an OK result code.
6 Included for compatibility only and has no effect other than returning an OK result code.

Command Syntax
AT&P[<value>]
Arguments
<value> Decimal number corresponding to the selected information.
0 Selects 39%-61% make/break ratio at 10 pulses per second. (Default.)
1 Selects 33%-67% make/break ratio at 10 pulses per second.
2 Selects 39%-61% make/break ratio at 20 pulses per second.
3 Selects 33%-67% make/break ratio at 20 pulses per second.


Command Syntax
ATL[<value>]
Arguments
<value> Decimal number corresponding to the selected option.
0 Off.
1 Low volume. (Default.)
2 Medium volume.
3 High volume.

Command Syntax
ATM[<value>]
Arguments
<value> Decimal number corresponding to the selected option.
0 Speaker off.
1 Speaker on during call establishment, but off when receiving carrier. (Default.)
2 Speaker on.
3 Speaker is off when receiving carrier and during dialing, but on during answering.

Article ID: 9
Last updated: 13 Oct, 2010
Revision: 1
Views: 26648
Comments: 0
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Tutorials     Configuring a Allen-Bradley SLC 500 PLC