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The modem includes a set of special or "S" registers that are used to
control the modem's behaviour. The contents of the S registers can be
altered to suit your needs and can be stored as part of a User profile
(see &W command).
Note: The default settings for your modem may differ from those listed
here. See the supplied Installation Guide for details of any
differences.
To alter the value of an S register the Sn=v command is used, where n is
the number of the register and v is the value. If a value outside the
range of the register is entered the modem sets the value to the nearest
maximum or minimum value. No ERROR message is generated. To view the
contents of a single register enter the Sn? command.
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S Register Descriptions
S0 Rings to Auto-Answer :
| Range : 0-255 |
Unit : Rings |
Default : 0 |
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This register (also known as the automatic answer enable register) determines the number of incoming rings the modem waits before answering the call. Setting the value to 0 disables the automatic answer facility and the A command must be issued to answer a call.
Example : ATS0=5 <Return> will cause the modem to answer after 5 rings.
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S1 Ring Counter :
| Range : 0-255 |
Unit : Rings |
Default : 0 |
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Register S1 maintains a running count of the incoming rings. This information is useful to software developers writing applications that utilise the modem in automatic answer mode.
The contents of the register are reset to zero when the modem answers an incoming call.
Note: This register is read only.
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S2 Escape Character :
| Range : 0-255 |
Unit : ASCII |
Default : 43 ('+') |
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The escape code character is, by default, the '+' symbol. However, this could cause problems with some remote systems and can be re-defined. Example: ATS2=37 <Return> causes the modem to recognise the '%' symbol as the escape code character. A value of greater than 127 prevents the escape code character from being recognised. A complete list of the ASCII character codes can be found in the back of this guide.
When the modem is being used to run a host system it may be wise to redefine the escape code character. For instance, the host system provides a remote echo facility for callers i.e. it echoes received characters back to the caller. The caller is running a modem with the AT command set. When the caller issues the escape sequence it is passed to the host system via the modem. The host system in turn echoes back the escape sequence to the caller via the modem. However, because the modem cannot distinguish between an escape sequence typed at the DTE and the echo of an escape sequence it goes into command mode. From this it can be seen that a change in the escape code character can be very useful!
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S3 Carriage Return <CR> Character :
| Range : 0-127 |
Unit : ASCII |
Default : 13 |
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The vast majority of computer systems rely on the standard ASCII character set to store textual information. Variations of this may require the use of a different character to represent <CR>.
Example: ATS3=10 <Return> sets the ASCII character 10 <LF> as the recognised <CR> character.
Here the original <Return> character was used to execute the command but from now on further commands must be terminated with the new value. i.e. <LF>
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S4 Line Feed <LF> Character :
| Range : 0-255 |
Unit : ASCII |
Default : 10 |
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Just as the <CR> character can be re-defined, so the <LF> character, by default ASCII 10, can be changed. This may be deemed necessary if the DTE inserts a line feed following a carriage return. For instance, when verbose result codes are in use, you may prevent the display of blank lines, if they occur, by setting the line feed character to NUL: ATS4=0 <Return>
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S5 Backspace <BS> Character :
| Range : 0-32 |
Unit : ASCII |
Default : 8 |
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Most computers or terminals use ASCII 127 (often marked DEL on the keyboard) to carry out the dual operation of backspacing and deleting incorrectly entered characters. The modem ALWAYS accepts ASCII 127 as delete.
However, some computers use ASCII 8 (backspace) in place of 127, although this does not usually delete the character concerned; it simply backspaces the cursor so that you can over type the incorrect character.
S5 contains a value which the modem accepts (in addition to ASCII 127) to effect a delete and is, by default, set to 8. If your computer uses any other character to represent delete or backspace, simply set S5 with the appropriate ASCII code.
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S6 Wait Time for Dial Tone :
| Range : 0-7 |
Unit : Seconds |
Default : 4 |
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Register S6 tells the modem how long to wait before attempting to dial
after grabbing the telephone line. The interpretation of the value in this register is dependent on the state of the dial tone detection command X.
With dial tone detection enabled (X2 or X4) the modem dials immediately after getting the dial tone, ignoring the status of S6. Disabling dial tone detection (X0, X1 or X3) forces the modem to blind dial, i.e. the modem dials regardless of the presence or absence of a dial tone, after the period specified in S6.
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S7 Wait Time for Carrier :
| Range : 0-58 |
Unit : Seconds |
Default : 40 |
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This register defines the time the modem waits for a remote carrier signal after dialling or answering. If the period specified has expired without detection of carrier, the NO CARRIER message is generated by the modem. If carrier is detected within the period, the modem negotiates a connection.
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S8 Pause Time for Dial Delay :
| Range : 1-10 |
Unit : Seconds |
Default : 2 |
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The inclusion of a "," (comma) in the dial string causes the modem to pause for the period specified before proceeding with the remainder of the dial string. Example : ATD 9 , 01234 567890 <Return>
In the example above the "," is used in place of the W command. This may be useful where the frequency of the secondary dial tone is such that it cannot be distinguished by the modem. In this example the modem dials 9, waits for 2 seconds (the default) then proceed to dial 01234 567890.
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S9 Carrier Detect Response Time :
| Range : 0-255 |
Unit : 0.1 seconds |
Default : 6 |
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The carrier detect time is the minimum period of time a remote carrier signal must be present on the line for it to be recognised as a valid carrier. The default is 6 representing 0.6 of a second. Reducing this value opens the way for spurious line noise to be interpreted as carrier thus causing premature connection.
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S10 Carrier Loss Disconnect Time :
| Range : 0-255 |
Unit : 0.1 seconds |
Default : 14 |
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Just as S9 is used to detect the time carrier must be present for it to be recognised as valid, so S10 works to determine the loss of carrier. If carrier is lost for a period exceeding the value in S10 the modem drops the line and goes on hook. This enables the filtering of any spurious line noise which may cause a disconnection. Setting S10 to 255 enables a special test mode that forces the modem to hold the line and generate carrier even when the remote carrier has been lost.
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S12 Escape Prompt Delay :
| Range : 0-255 |
Unit : 0.02 seconds |
Default : 50 |
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The escape sequence guard time defines the period of time before and after the escape sequence (and the period between each character of the sequence) in which no other characters can be transmitted for it to be recognised as the escape sequence.
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S14 General Bit Mapped Options Status :
| Range : - |
Unit : - |
Default : 138 |
A Bit mapped option register allows you to check the current settings of
various commands. You would not normally alter this register directly
because it is easier to use the actual commands themselves. The function
of this register is coded in binary and displayed in decimal.
| Bit 0
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This bit is ignored.
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| Bit 1
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Command echo (En)
0 = Disabled (E0)
1 = Enabled (E1) (Default.)
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| Bit 2
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Quiet mode (Qn)
0 = Send result codes (Q0) (Default.)
1 = Do not send result codes (Q1)
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| Bit 3
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Result codes (Vn)
0 = Numeric (V0)
1 = Verbose (V1) (Default.)
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| Bit 4
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Reserved
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| Bit 5
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Tone (T)/Pulse (P)
0 = Tone (T) (Default.)
1 = Pulse (P)
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| Bit 6
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Reserved
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| Bit 7
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Originate/Answer
0 = Answer
1 = Originate (Default.)
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S16 General Bit Mapped Test Options Status :
| Range : - |
Unit : - |
Default : 0 |
A Bit mapped option register allows you to check the current settings of
various commands. You would not normally alter this register directly
because it is easier to use the actual commands themselves. The function
of this register is coded in binary and displayed in decimal.
| Bit 0
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Local analog loopback
0 = Disabled (Default.)
1 = Enabled (&T1)
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| Bit 1
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Not used
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| Bit 2
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Local digital loopback
0 = Disabled (Default.)
1 = Enabled (&T3)
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| Bit 3
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Remote digital loopback (RDL) status
0 = Modem not in RDL (Default.)
1 = RDL in progress
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| Bit 4
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RDL requested (AT&T6)
0 = RDL not requested (Default.)
1 = RDL requested (&T6)
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| Bit 5
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Bit 5 RDL with self test
0 = Disabled (Default.)
1 = Enabled (&T7)
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| Bit 6
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Local analog loopback (LAL) with self test
0 = Disabled (Default.)
1 = Enabled (&T8)
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| Bit 7
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Not used
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S18 Test Timer :
| Range : 0-255 |
Unit : Seconds |
Default : 0 |
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Register S18 is used to set the time duration of the loopback tests performed by the modem. After this period, the test is terminated and the modem returns to local mode. The default value of 0 causes the test to be conducted continuously until terminated by the &T0 or H0 command.
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S20 AutoSync HDLC Address or BSC Sync Character :
| Range : 0-255 |
Unit : - |
Default : 0 |
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Defines the HDLC address (S19 bit 1 = 1) or BSC Sync Character (S19 bit 1 = 0) for AutoSync operation (see &Q4
command). S20 must be set to the desired value before &Q4 is issued.
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S21 V.24/General Bit Mapped Options Status :
| Range : - |
Unit : - |
Default : 52 |
A Bit mapped option register allows you to check the current settings of
various commands. You would not normally alter this register directly
because it is easier to use the actual commands themselves. The function
of this register is coded in binary and displayed in decimal.
| Bit 0
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Set by &Jn command but ignored otherwise.
0 = &J0 (Default.)
1 = &J1
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| Bit 1
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Reserved
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| Bit 2
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CTS behavior (&Rn)
0 = CTS tracks RTS (&R0)
1 = CTS always on (&R1) (Default.)
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| Bits 3-4
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DTR behavior (&Dn)
0 = &D0 selected
1 = &D1 selected
2 = &D2 selected (Default.)
3 = &D3 selected
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| Bit 5
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RLSD (DCD) behavior (&Cn)
0 = &C0 selected
1 = &C1 selected (Default.)
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| Bits 6
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DSR behavior (&Sn)
0 = &S0 selected (Default.)
1 = &S1 selected
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| Bits 7
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Bit 7 Long space disconnect (Yn)
0 = Y0 (Default.)
1 = Y1
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S22 Speaker/Results Bit Mapped Options Status :
| Range : - |
Unit : - |
Default : 118 |
A Bit mapped option register allows you to check the current settings of
various commands. You would not normally alter this register directly
because it is easier to use the actual commands themselves. The function
of this register is coded in binary and displayed in decimal.
| Bits 0-1
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Speaker volume (Ln)
0 = Off (L0)
1 = Low (L1)
2 = Medium (L2) (Default.)
3 = High (L3)
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| Bits 2-3
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Speaker control (Mn)
0 = Disabled (M0)
1 = Off on carrier (M1) (Default.)
2 = Always on (M2)
3 = On during handshake (M3)
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| Bits 4-6
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Limit result codes (Xn)
0 = X0
4 = X1
5 = X2
6 = X3
7 = X4 (Default.)
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| Bit 7
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Reserved
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S23 General Bit Mapped Options Status :
| Range : - |
Unit : - |
Default : 190 |
A Bit mapped option register allows you to check the current settings of
various commands. You would not normally alter this register directly
because it is easier to use the actual commands themselves. The function
of this register is coded in binary and displayed in decimal.
| Bit 0
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Grant RDL
0 = RDL not allowed (&T5) (Default.)
1 = RDL allowed (&T4)
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| Bits 1-3
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DTE Rate
0 = 0 - 300 bps
1 = 600 bps
2 = 1200 bps
3 = 2400 bps
4 = 4800 bps
5 = 9600 bps
6 = 19200 bps
7 = 38400 bps or higher (Default.)
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| Bits 4-5
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Assumed DTE parity
0 = even
1 = not used
2 = odd
3 = none (Default.)
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| Bits 6-7
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Guard tone (&Gn)
0 = None (&G0)
1 = None (&G1)
2 = 1800 Hz (&G2) (Default.)
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S25 Delay to DTR Off :
| Range : 0-255 |
Unit : 0.01 seconds (async); seconds (sync) |
Default : 5 |
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S25 sets the length of time that the modem ignores DTR before hanging up. The units of this value change for synchronous and asynchronous modes.
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