Issue 146 September 2002
Internet Enabling Made Easy

2124 EVALUATION BOARD

The 2124 modem is much like an integrated circuit in that you simply plug it into a socket and use its internal functionality by interfacing external signals with its pins. If you need to develop and certify a new 2124 modem application, you should purchase a 2124 evaluation board.

The advantages of the evaluation board include: on-board RS-232 terminal interface circuitry; a regulated +5-VDC power supply; a protected RJ-11 telephone line interface; audio circuitry for easy audible call progress monitoring; call and modem status LEDs; call status indicator circuitry; a Reset button; an e-mail Send button; an e-mail Status Clear button; and all of the 2124 signals brought out to standard 0.1² center header pins.

You can incorporate jumpers to route the modem control signals to the on-board RS-232 circuitry if your application requires it. Using the 2124 evaluation board jumpers and signal pins allows the hardware and software designer to extend the 2124 signals off of the evaluation board to custom external electronics. In addition, you can prove concepts and design ideas before incurring the cost of preproduction or prototype printed circuit boards.

It isn’t too difficult to begin developing with the 2124 modem. First, you have to plug in the included wall transformer and attach a phone line. Then, connect a user-supplied RS-232 interface cable between your PC and the 9-pin serial connector on the evaluation board. After that’s done, you can power up the evaluation board.

If the default values aren’t to your liking, a simple iNetWizard procedure allows you to enter the destination e-mail address and ISP phone number of your choice. By pressing the e-mail Send button you will immediately pick up the phone and send a preloaded e-mail message to the destination you selected with iNetWizard.

Depending on the application, visual call progress status may or may not be required. If you need visual feedback on your custom 2124 modem system board, the call status can be captured with simple D-type latches or a small area of logic inside a programmable logic device (PLD) and displayed via LEDs. Take a look at Figure 1 to see how the e-mail sent event could be captured and displayed.

Figure 1—There isn’t any rocket science here. You can catch most of the CH2124’s event signals with this simple circuit.

You can also sense the call status with an external microcontroller, which gives you almost unlimited flexibility in reacting to the call progress indicators. A bare evaluation board and a 2124 evaluation board loaded with a 2124 modem are displayed in Photo 2.

Photo 2a—Everything you would design into a home-brewed modem development board can be found on the Cermetek 2124 evaluation board. Included are power, phone line, and terminal interfaces, as well as status LEDs and a speaker. b—And now, take a look at the board without the modem. Note the layout of the modem module pins. The backside of the evaluation board supports the MAX237 RS-232 IC and some surface mount glue logic.