Black Box MD1276A, User Manual

Page: 49 / 289

AT Commands
Page 49
+ Data should only be transmitted once DCD, DTR and CTS have been asserted.
Your computer should not assume that if CTS is asserted then it is safe to begin
transmitting data
—
your modem will keep CTS asserted whenever it is in local
command state.
Hanging Up
Your modem will hang up and return to asynchronous mode if carrier is lost for longer than the
period defined by S Register 10 or if DTR is lowered after the &D2 command has been issued.
Answering Calls
To automatically answer incoming calls, S Register 0 must be set to a non-zero value (as with
asynchronous auto-answering). Once a call has been answered there is no means of returning to
asynchronous mode apart from hanging up the modem. This will occur if the carrier is lost for a
period in excess of the time defined by S Register 0 or if DTR is lowered after the &D2
command has been issued.
Synchronous Mode 2
Synchronous mode 2 is specifically designed for use with dedicated synchronous terminals. The
phone number to be dialed is stored in the modem, the synchronous terminal causing the modem
to dial by asserting the DTR signal.
When the terminal asserts the DTR signal (DTR makes an OFF-ON transition), your modem
will dial stored phone number zero. The phone number may contain dial modifiers. See the
Command Descriptions chapter of this guide for details on the &Z command.
Before connecting your modem to your synchronous terminal, the modem must first be
configured using an asynchronous terminal or computer. The Sample Setups section of this
manual details a common configuration for synchronous mode 2.
Selecting Synchronous Mode 2
Synchronous mode 2 is selected with the &M2 command.
•
Type: AT&M2 <E>
Your modem will enter synchronous mode whenever it successfully connects to a remote
modem.
You should also:
•
Type: AT&D2 <E>
This allows you to dial and hang up.
To return to asynchronous mode:
•
Type: AT&M0 <E>
Your modem will remain in asynchronous mode.