S Registers

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).

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.

S Register Descriptions
S0 Automatic answer control :

Range : 0-255 Unit : Rings Default : 0
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.

S1 Ring counter :

Range : 0-255 Unit : Rings Default : 0
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.

S2 ASCII value of escape character :

Range : 0-255 Unit : ASCII Default : 43 ('+')
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!

S3 ASCII value of carriage return <CR> character :

Range : 0-127 Unit : ASCII Default : 13
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>

S4 ASCII value of line feed <LF> character :

Range : 0-127 Unit : ASCII Default : 10
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>

S5 ASCII value of backspace <BS> character :

Range : 0-127 Unit : ASCII Default : 8
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.

S6 Dial tone wait time :

Range : 2-65 Unit : Seconds Default :2
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.

S7 Carrier wait time :

Range : 1-255 Unit : Seconds Default : 50
This register defines the time, in seconds, that the modem must wait before hanging up because carrier is not detected. The timer is started when the modem finishes dialling (originate), or goes off-hook (answer). In originate mode, the timer is reset upon detection of answer tone if allowed by country restrictions. This timer also specifies the wait for silence time for the @ dial modifier in seconds. S7 is not associated with the W dial modifier. 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.

S8 Dial pause time :

Range : 0-65 Unit : Seconds Default : 2
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.

S10 Carrier loss delay :

Range : 1-254 Unit : 1/10th seconds Default : 20
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.

S11 DTMF Duration and Interdigit Delay :

Range : 50-150 Unit : 1/1000th seconds Default : 95

S12 Escape sequence guard time :

Range : 0-255 Unit : 1/50th seconds Default : 50
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.

S14 Bit-Mapped Options Status:
Default : 8 (00001000b)

Bit 3 Result codes (Vn); 0 = Numeric (V0); 1 = Verbose (V1) (Default).
Bit 6 Pulse dial PPS selection (&Pn); 0 = 10 PPS (&p0, &p1) (Default).

S21 V.24/General Bit-Mapped Options Status:
Default : 48 (00110000b)

Bits 3-4 DTR Behaviour (&Dn)
0 = &D0 Selected
1 = &D1 Selected
2 = &D2 Selected ( Default)
3 = &D3 Selected
Bit 5 DCD Behaviour
0 = &C0 Selected
1 = &C1 Selected (Default)

S22 Results Bit-Mapped Options Status:
Default : 112 (01110000b)

Bits 4-6 Result Codes (Xn)
0 = X0 Selected
4 = X1 Selected
5 = X2 Selected
6 = X3 Selected
7 = X4 Selected (Default)
Bit 7 Pulse Dial make/break ratio (&Pn)
0 = 33/67 make/break ratio (&P1, &P2) (Default)
1 = 39/61 make/break ratio (&P0)

S24 Timer to control Sleep Mode

Range : 0,5-65 Default : 10
S24 This command displays the number of seconds of inactivity in the off line command state before the modem places itself in standby mode.

S28 V.34 Modulation Enable/Disable

Range : 0-1 Default : 1
S28 enables/disables V.34 modulation. 0 = disabled, 1 = enabled

S30 Inactivity timer :

Range : 0-255 Unit : Minutes Default : 0

S32 Synthetic Ring Volume

Range : 0-255 (Allowed but not meaningful) Default : 10
S28 specifies a synthetic ring volume

S33 Synthetic Ring Frequency

Range : 0-5 Default :0
This register specifies a Synthetic ring frequency. There are 5 to choose from with 0 being disabled

S35 Data Calling Tone

Range : 0-1 Default : 0
Data calling tone is a tone of particular frequency and cadence as specified in V.25 which allows Data/Fax/Voice discrimination. The frequency is 1300Hz with a cadence of .5s on and 2s off. 0 = Disabled, 1 = enabled.

S37 Dial Line Rate (default 0)

This register sets the maximum line data rate. In K56flex and V.90 mode, S37 controls the upstream V.34 rate.

0 = Autorate 10 = Attempt a 12000 bit/s connection
1 = Reserved 11 = Attempt a 14400 bit/s connection
2 = Attempt a 1200/75 bit/s connection (V.25) 12 = Attempt a 16800 bit/s connection
3 = Attempt a 300 bit/s connection 13 = Attempt a 19200 bit/s connection
4 = Reserved 14 = Attempt a 21600 bit/s connection
5 = Attempt a 1200 bit/s connection 15 = Attempt a 24000 bit/s connection
6 = Attempt a 2400 bit/s connection 16 = Attempt a 26400 bit/s connection
7 = Attempt a 4800 bit/s connection 17 = Attempt a 28800 bit/s connection
8 = Attempt a 7200 bit/s connection 18 = Attempt a 31200 bit/s connection
9 = Attempt a 9600 bit/s connection 19 = Attempt a 33600 bit/s connection

S43 Auto mode (error corrected modes only) :

Default : 1
Used for testing and debugging only.V.32bis startup auto mode operation disabled. 0 = auto mode disabled, 1 = enabled.

S90 Read Only local Phone

Default : 1
This register tells the status of the local phone. It is read only. 0 = on-hook 1 = off-hook

S38 Downstream rate selection for V.90 mode

0 = V.90 Disabled 12 = 42666
1 = V.90 Autorate 13 = 44000
2 = 29333 14 = 45333
3 = 30666 15 = 46666
4 = 32000 16 = 48000
5 = 33333 17 = 49333
6 = 34666 18 = 50666
7 = 36000 19 = 52000
8 = 37333 20 = 53333
9 = 38666 21 = 54666
10 = 40000 22 = 56000
11 = 41333


S109 - Automode selection:  
0  V.PCM Disabled 
1  K56 or V.90 
2  V.90 Only (K56flex disabled) 

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