&Q n - Select Communications Mode Option


Command Line Format
AT [cmds] &Q [suffix] [cmds] <CR>

Suffix Values
0-6, 8-10

Default
&Q5

Stored by &Wn
yes

Displayed by &V
yes

Description
The &Q command selects the communication mode and is the extended version of the &M command. The &Q command determines how the modem treats transmitted and received data while in the Online state (i.e., asynchronous, synchronous, AutoSync, error-control, or buffered asynchronous) and establishes certain call setup procedures. Refer also to the &Cn, &Dn, and &Sn commands, and to the Dialing, Answer sections.

The &Q2 and &Q3 commands enable synchronous terminals to use the modem. The modem is configured by an asynchronous DTE, while DTR is off. Then the synchronous terminal is connected to the modem and calls are controlled by DTR as described below. If the value of S0 is not 0, and ringing is detected, then after DTR goes on, the modem answers the call when the following conditions are satisfied: (1) after the next ring and (2) when the value of S1 equals or exceeds that of S0.

Note: Detection of ringing is forgotten by the modem if ringing is not detected for 8 seconds. Because of the intended use by synchronous terminals, the A (answer) and D (dial) commands are invalid when either &Q2 or &Q3 is selected. The modem sends the ERROR result code if it receives an A or D command (which would have to occur while DTR is off).

All of the &Qn commands are valid in the offline command state; none are valid in the Online Command State (return ERROR).
&Q0 Asynchronous
RLSD, DSR, and DTR behaviors are unique. (Refer to &Cn, &Sn and &Dn command definitions).
&Q1 Synchronous
In smart and switched dumb mode, DTR must be ON after CONNECT when a timer equal to S25 expires. DTR is ignored in dumb leased-line mode.

&Q2 Synchronous
DTR OFF-to-ON executes Dialing Process; with the D command invalid. DTR is ignored in dumb leased-line mode. DTR ON-to-OFF executes Hangup Process (or the Reset Process if &D3 is in effect). The A command is invalid.

&Q3 Synchronous
Dialing and Voice allowed from telephone when DTR is OFF. DTR is ignored in dumb leased-line mode. DTR OFF-to-ON executes the Handshaking Process (in originate mode); the D command is invalid. DTR ON-to-OFF executes Hangup Process (or the Reset Process if &D3 is in effect). The A command is invalid.

&Q4 Hayes AutoSync
If AutoSync is in effect, DTR must be ON after CONNECT when timer equal to S25 expires; AutoSync II does not wait for S25 time settings to check DTR. Refer to the &Dn command for other DTR behaviors in &Q4 mode and refer to the AutoSync and AutoSync II specifications for other details of how S25 affects modem operation.

&Q5 Error-Control
This enables error-control. Depending upon various other commands, any one of several point-to-point protocols may be negotiated. After the modem handshake is complete, feature negotiation (see S48) determines which protocol (see S46) is used for the communication session. If no common protocol is found between the local and remote modems, the fall back option (see S36) is used. These may include Automatic Speed Buffering (ASB), asynchronous mode or going on-hook. When in &Q5 mode, the DTE is always presented an asynchronous interface. When either error-control or ASB has been negotiated, flow control (&Kn) should not be disabled. The &Q1, &Q2, &Q3, and &Q4 commands return ERROR when issued while online during an error-control or ASB connection.

&Q6 Buffered Asynchronous
Automatic Speed Buffering is useful for DTEs which cannot adjust to changing transmission speeds. This mode ensures the DTE-modem speed is set at a constant rate regardless of the line speed determined during the modem handshake. With the exception of flow control (&Kn) between the DTE and the attached modem, this mode is identical to the standard asynchronous mode (&Q0). ASB operation is also a fall back option (see S36) when the modem is set for error-control mode (&Q5). With DTE and DCE speeds being different in ASB, a buffer is provided so that flow control does not occur on every character transmission. Some DTEs are sensitive to the buffer size so S-registers are provided to control the lower (S49) and upper (S50) boundaries.
&Q8 MNP Error-Control

The modem attempts to negotiate an MNP error-control link upon connection. The current setting in S46 bit 1 determines whether MNP2-4 or MNP5 is negotiated. If S46 bit 1 is set to 1, MNP5 is preferred. If an MNP error-control protocol is not established, the modem falls-back according to
the current setting in S36. The settings in S48 and S46 (except bit 1) are ignored. If fallback to Buffered Async mode occurs, all data received during protocol negotiations are present in the received data buffer.

&Q9 V.42bis/MNP2-4 Error-Control
The modem attempts to negotiate a V.42bis error-control and V.42bis compression link upon connection. If V.42bis (or V.42) is not achieved, then MNP2-4 is attempted. If neither error-control protocol is established, the modem falls-back according to the current setting in S36. If S36 bit 0 is 0 the modem hangs-up. If S36 bit 0 is 1 the modem connects according to S36 bit 1. If S36 bit 1 is 0 the modem connects in Direct Async mode. If S36 bit 1 is 1 the modem connects in Buffered Async mode. The settings in S48 and S46 are ignored. If fall-back to Buffered Async mode occurs, all data received during protocol negotiations is present in the received data buffer.
&Q10 X.25 Error-Control

The modem makes an X.25 connection by first establishing a synchronous connection and immediately attempting a link layer establishment after which a packet layer establishment attempt will transpire. If the X.25 connection attempt is successful, you will then be given access to the XXX PAD to place and/or receive virtual calls. If the X.25 connection attempt is not achieved, the modem will hang up. The following points apply when using &Q10: As in all error-control or buffered modes, &Kn determines the type of local flow control.

DTE Interface Lines Affected
DSR, RLSD

References Commands
&Cn, &Dn, &Sn, &Kn, Nn - Select Negotiate Handshake Option

S-Registers:

S36 - Negotiation Fall Back

S37 - Desired DCE Line Speed

S46 - Protocol Selection

S48 - Feature Negotiation Action

S49 - ASB Buffer: Low Boundary

S50 - ASB Buffer: High Boundary

DTE signals - DSR,DTR,RLSD

Lamps - TR

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