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Attaching a Hayes Compatible Modem to the EX Switch Console Port



Article ID: KB20981 KB Last Updated: 29 Sep 2020Version: 4.0

The purpose of this article is to provide the steps required to attach a Hayes Compatible Modem (US Robotics v.34 28800 Sportster) to the EX Switch console port.

This article will walk you through the setup of a US Robotics 28800 v.34 Sportster modem connected to the EX Switch console port.  It is also important to note the EX Switch configuration for the console port, "log-out-on-disconnect", which logs out the user session on carrier detect dropping.  

This article will walk you through the setup of a US Robotics 28800 v.34 Sportster modem connected to the EX Switch console port.


[LAPTOP/Modem]---<PSTN>---[USR modem]----[EX Switch Console Port]


  • Laptop/Modem
  • US Robotics 28800 v.34 modem (Hayes Compatible Modem so later models should work the same)
  • CM Cable Adapter DB25M (Digi PN 76000672) - DB25 to RJ45 terminal adaptor (modem terminal DB25)
  • Standard telephone cable RJ-11
  • Standard Cat 5e cable
  • Analog lines (POTS)
  • Terminal Application such as HyperTerminal

Modem configuration

PC or Laptop Setup:
  1. Connect the modem to the PC or Laptop computer using HyperTerm application (common to Windows) or some other terminal program.
  2. Set Dip Switches to: (1-7 UP) (8 DOWN)
  3. Power on the modem
  4. From the computer, start your asynchronous terminal emulation application and select the COM port to which the modem is connected.
  5. Configure the port settings:
    BPS = 9600
    Data Bits = 8
    Parity = None
    Stop bits = 1
    Flow Control = None
  6. Copy and paste to modem - AT&F0Q1E0S0=1&H0&I&R1&B1&D0&W (Hit Enter)
  7. Power down modem
  8. Set Dip Switches to: (2,3,5,7 UP) (1,4,6,8 DOWN)

Standard USR Modem Dip Switches - Reference

Switch Factory Function
  1. Data Terminal Ready (DTR) Override

    (UP) Data Terminal Ready Normal - Normal DTR operations: computer must provide DTR signal for the modem to accept commands; dropping DTR terminates a call
    (DOWN) DTR Override - Modem ignores DTR (Override)
  2. Verbal/Numeric Result Codes

    (UP) Verbal (word) result codes
    (DOWN) Numeric result codes
  3. (Result Code Display

    (UP) Suppresses result codes
    (DOWN) Enables result codes
  4. Command Mode Local Echo Suppression

    (UP) Displays keyboard commands - Echo offline commands
    (DOWN) Suppresses echo - No echo, offline commands
  5. Auto Answer Suppression

    (UP) Modem answers on first ring, or higher if specified in NVRAM
    (DOWN) Suppress/Disables auto answer
  6. Carrier Detect (CD) Override

    (UP) Carrier Detect Normal - Modem sends CD signal when it connects with another modem, drops CD on disconnect
    (DOWN)  Carrier Detect Override - CD always ON (Override)
  7. Power-on and ATZ Reset Software Defaults

    (UP) Load NVRAM defaults - Loads Y0-Y4 configuration from user-defined nonvolatile memory (NVRAM)
    (DOWN) Load Factory Defaults - Loads &F0¾Generic template from read only memory (ROM)
  8. AT Command Set Recognition

    (UP) Dumb Mode - Disables command recognition (dumb mode)
    (DOWN) Smart Mode - Enables recognition (smart mode)

To automatically log out a session on the EX Switch when:

  • Modems disconnect
  • Session is disconnected by hang-up
  • Physical cable between modem and the EX Switch console port is disconnected

Configure the following on the EX Switch:

# set system ports console log-out-on-disconnect

NOTE: The configuration variable "log-out-on-disconnect" logs out the session when the data carrier on the console port is lost.

NOTE: Carrier Detect (CD) Override should be disabled so that "Modem sends CD signal when it connects with another modem, drops CD on disconnect."
With above configuration this is Dip Switch number 6 in the DOWN position.
CD must drop on disconnect or your login session will NOT be logged out (ie: log-out-on-disconnect).

RJ-45 to DB-25 Console Adaptor Pinouts (Adaptor used Digi CM, PN: 76000672)

Specifications for the NULL MODEM cable

The following pinout is consistent with a DB9-DB25 converter cable with the exceptions of pins 2 and 3.

Assumes DB9 Plug to DB25 Plug

DB9     DB25
1             8
2             2
3             3
4            20
5             7
6             6
7             4
8             5
9            22

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