Black Box MD1640A, MD1641A manual Modem Testing, Local Analog Loopback Test/V.54 Loop

CHAPTER 8: Modem Testing

8.2 Local Analog Loopback Test/V.54 Loop 3

In this test, data from your computer or terminal is sent to your modem's transmitter, converted into analog form, looped back to the receiver, converted into digital form and then received back at your monitor for verification. No connection to the phone line is required. See Figure 8-1.

Computer or Terminal

UUUUU UUUUU

Local Series II Modem

digital analog

Type ATU0 or ATU1; hit ENTER

Figure 8-1. Local Analog Loopback Test

The test procedure is as follows:

1.Connect the modem to your computer. With your communication software, set the desired baud rate.

2.Type ATU0 (or ATU) and hit ENTER. This places your modem in Analog Loopback mode, in the Originate mode. The modem is now out of the Command mode and in a pseudo On-Line mode.

3.Once you receive a connect message (if responses are enabled), enter data from your keyboard. For this test, typing multiple upper case "U" characters is a good way to send an alternating test pattern of ones and zeros.

4.For a more complete test, you should also test the modem in Answer mode. To do this, you must “escape” from Originate mode by entering an Escape Sequence (+++AT<CR> or <BREAK>AT<CR>) . Then type ATU1 and hit ENTER to place the modem in Analog Loopback mode, in the Answer mode. Then repeat step 3.

117