Multi-Tech Systems MTS2SA-T - Manual (Page 99)

Chapter 10
− Modem Mode AT Commands, S-Registers, and Result Codes
Multi-Tech Systems, Inc. MultiConnect Serial-to-Serial Adapter User Guide (S000354A) 99
Case 3: Telephone Line is Not Connected to Modem
If an ATDT, ATDP or ATDL is issued while Line-In-Use detection is enabled and the
telephone line is not connected, the modem will go off-hook momentarily, go back on-
hook, then respond with NO DIAL TONE message.
Extension Pick-up (Enabled by AT-STE=2, AT-STE=3, AT-STE=6, or AT-STE=7):
Case 1: Modem off-hook, Local Handset Goes Off-Hook
If the local handset goes off-hook while the modem is in a data connection, the local
handset will be muted. The modem will then send a GSTN Cleardown to the remote
modem and then go on-hook. The modem will then send a NO CARRIER message to
the DTE. A result code of 25 will be left in S86 register. After 2 seconds, the local
handset will be connected to the telephone line so the user hears the dial tone.
Case 2: Modem off-hook, Extension Pick-up
If the modem is connected and another extension goes off-hook, the modem will send a
GSTN Cleardown to the remote modem and then immediately hang-up. Due to the noise
possibly being added to the line when a telephone extension is picked-up, a GSTN
Cleardown may or may not successfully be received by the remote mode. If the GSTN
Cleardown is not received successfully by the remote modem, the remote modem may
attempt a retrain until the retrain fails and the remote modem drops the line. In any case,
the modem will send a NO CARRIER message to the DTE immediately after sending the
GSTN Cleardown. Result code 25 will be left in the S86 register.
Because the extension is off-hook, the modem cannot flash the hook for the central
office to generate a dial tone. In this case, the user must flash the extension handset to
obtain a dial tone.
Remote Hang-up (enabled by AT-STE=4, AT-STE=5, AT-STE=6, or AT-STE=7):
Case 1: Modem off-hook, Remote Hang-up
If the modem is connected (off-hook) and the remote modem/server goes hangs up, the
central office may issue a line polarity reversal. If a line polarity reversal is detected, the
modem will drop the call and respond with NO CARRIER. The reason for hang-up can
be determined by #UD or by S86=25. A line reversal can also be simulated by simply
pulling out the telephone line during a connection.
Command:
%Cn Enable/Disable Data Compression Control (Not available in V.22 bis)
Values: n = 0, 1, 2, 3
Default: 3
Description:
Enables or disables data compression negotiation. The modem can only perform data
compression on an error-corrected link. The parameter value, if valid, is written to S41 bits 0
and 1.
%C0 Disables data compression. Resets S46 bit 1.
%C1 Enables MNP 5 data compression negotiation. Resets S46 bit 1.
%C2 Enables V.42 bis data compression. Sets S46 bit 1.
%C3 Enables both V.42 bis and MNP 5 data compression. Sets S46 bit 1. (Default.)
Command:
%En Enable/Disable Line Quality Monitor and Auto-Retrain
Values: n = 0, 1, 2
Default:
2 (default is 1 in V.22bis)
Description: Controls whether or not the modem will automatically monitor the line quality and request a
retrain (%E1) or fall back when line quality is insufficient or fall forward when line quality is
sufficient (%E2). The parameter value, if valid, is written to S41 bits 2 and 6.
If enabled, the modem attempts to retrain for a maximum of 30 seconds.
%E0 Disable line quality monitor and auto-retrain (disable fallback and fall forward).
%E1 Enable line quality monitor and auto-retrain (enable fallback, disable fall forward).
%E2 Enable line quality monitor and fallback/fall forward (enable fallback and fall forward).
(%E2 is not available in V.22bis)
Fallback/Fall Forward. When %E2 is active, the modem monitors the line quality (EQM).
When line quality is insufficient, the modem will initiate a rate renegotiation to a lower speed
within the V.34/V.32 bis/V.32 (RC336) modulation speeds. The modem will keep falling back
within the current modulation if necessary until the speed reaches 2400 bps (V.34) or 4800
bps (V.32). Below this rate, the modem will only do retrains if EQM thresholds are exceeded.
If the EQM is sufficient for at least one minute, the modem will initiate a rate renegotiation to
a higher speed within the current modulation speeds. The rate renegotiations will be done
without a retrain if a V.32bis connection is established.
Speeds attempted during fallback/fall forward are those shown to be available in the rate
sequences exchanged during the initial connection. Fallback/fall forward is available in error
correction and normal modes, but not in direct mode or synchronous mode with external
clocks.