Black Box MD1640A, MD1641A manual Digital Loopback Test Remote/Automatic Synchronous Mode

CHAPTER 8: Modem Testing

data passed from the remote modem’s transmit circuit are looped back from the local modem and are received at the remote modem’s receive circuit (multiple upper case “U” characters in Figure 8-6).

First make certain that you are set up for Synchronous operation by placing DIP-Switch #12 in the UP position. To initiate the Digital Loopback Test (local/manual), DIP-Switch #9 must be in the UP position, and the Answer/Originate switch (front of the modem) must be toggled to the UP position. Once you receive an OK message from your modem (if responses are enabled), the local modem is placed in Digital Loopback mode.

To exit the Digital Loopback Test (local/manual), toggle the Answ/Orig switch to the Answer position.

Computer							Computer
or Terminal							or Terminal
	Local Series II			Remote Series II
		Modem			Modem
								UUUUU
	digital		analog	analog		digital		UUUUU

DIP switch #9 UP; Answ/Orig switch toggled to Answ position when On-line

Figure 8-6. Synchronous Mode Digital Loopback Test

(local/manual)

8.9Digital Loopback Test (Remote/Automatic) (Synchronous Mode)

This test must be run when you have a data connection with another modem. In this test, data is passed to the remote modem and is looped back to the local modem (as if an ATU2 command was issued in Asynchronous test mode), as shown in Figure 8-7. This lets you test the local and remote modem’s transmit and receive circuits, as well as your computer’s serial COM port and the phone lines. If the test results in a mismatch of entered/received data (multiple upper case “U” characters

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