Testing MBus for Nokia 3310

Once you have built the Nokia 3310 MBus circuit, it is very simple to test it without requiring connection to the phone. The test requires connection to the COM1 port of the computer, or a compatible serial port that the computer has. It also requires the use of HyperTerminal, which is readily available software found on many operating systems.

The way HyperTerminal works is that when you type characters, this data passes out through the serial port, and any character received through the serial port displays in the window. Since the diode D5 loops the characters sent out back into the serial port, what you type in HyperTerminal is visible on the screen proving that the circuit works. If you are able to see these echoed characters, then it means that the circuit is operating correctly for the most part. For this test, the jumper J1 position must be in the top position for serial (MBus) communications. Make sure your serial port COM1 is working and you know which it is at the back of the computer.

Does COM Port Exist?

First, check the "Device Manager" in "Control Panel" and check if the serial port drivers exist. If you do not see "Communications Port (COM1)" then you need to investigate why your computer does not have this port.

COM1 Port Settings

Our circuit uses only the Tx and Rx pins for communication. No other control signals are used; therefore, the "Flow Control" parameter is set to "None".

HyperTerminal Setting

As you can see, this software may also require you to set additional parameters in its window. In this window, the "COM1" parameter is required.

HyperTerminal Call

Once you have mastered the use of HyperTerminal and have it configured properly, you initiate a connection using the "Call" option in the menu. When you type letters on the keyboard, those characters echo back and display on the screen. If you cannot see the echoed letters you typed, then you need to test your COM1 port by joining pin 2 and pin 3 on COM1 and running HyperTerminal again as shown in the above steps. If this works then, the COM1 port is fully functional and you need to focus on the circuit.

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