3Com 56K manual Using AT&T8

14-4CHAPTER 14: TESTING THE CONNECTION

If you use the S18 test timer, but in the process of testing you issue an ATZ command, S18 resets to zero and the timer is disabled. You cannot store a value for S18 in NVRAM; its power-on and reset default is always zero.

	Using AT&T8
	This analog loopback option causes the Business Modem to send an
	internal test pattern to its transmitter and loop it back to the receiver. An
	internal error detector counts any errors and, when the test is ended,
	sends the number of errors or 000 (no errors) to the screen.
	Since you don't type anything during this test, and the Business Modem
	does not send anything to the screen, this option verifies only the
	Business Modem. If there are no errors but your problem continues, it
	may be at the computer interface.
1	Send AT&M0&N3S14.0=0 to the modem prepare for testing.
	This command disables error control, fixes the connection rate at 2400
	bps, and makes the Business Modem return to command mode when
	you type +++.
2	Send AT&T8 to begin the test.
	The Business Modem enters analog loopback (AL) mode, and sends a
	CONNECT message. The MR status light flashes. The V.Everyhing then
	sends its internal test pattern to the transmitter, and loops the pattern
	back to the receiver. You will not see any data on your screen.
3 Send the escape code, +++, and then AT&T0 to end the test.
	Alternatively, you can end the test by sending ATH or ATZ. Be careful,
	because ATZ resets the modem in addition to ending the test.
	In any case, the Business Modem hangs up and returns a three-digit
	code, followed by OK.
	The code	Indicates
	000	No errors were found
	255	255 or more errors

An ERROR message indicates that you issued an invalid command.

4Send AT&M4, unless you used a reset command (ATZ or ATZ!).