S-Registers

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# B.4. S-Registers

Table B-4. S Registers

Register | Range | Default | Function
--- | --- | --- | ---
`S0` | 0-255 rings | 1-2 | Answer on ring number. Don't answer if 0
`S1` | 0-255 rings | 0 | if `S0` is greater than 0 this register counts the incoming rings.
`S2` | 0-127 ASCII | 43 + | Escape to command mode character
`S2` | >127 |  | no ESC
`S3` | 0-127 ASCII | 13 CR | Carriage return character
`S4` | 0-127 ASCII | 10 LF | Line feed character
`S5` | 0-32, 127 ASCII | 8 BS | Backspace character
`S6` | 2-255 seconds | 2 | Dial tone wait time (blind dialling, see X`n`
`S7` | 1-255 seconds | 30-60 | Wait time for remote carrier
`S8` | 0-255 seconds | 2 | Comma pause time used in dialing
`S9` | 1-255 1/10ths second | 6 | Carrier detect time required for recognition
`S10` | 1-255 1/10ths second | 7-14 | Time between loss of carrier and hangup
`S11` | 50-255 milliseconds | 70-95 | Duration and spacing of tones when tone dialing
`S12` | 0-255 1/50th seconds | 50 | Guard time for pause around +++ command sequence
`S36` | Fallback options when error correction link fails: 0 - Disconnect 1 - Establish Direct Connection 3 - Establish Normal Connection 4 - Establish an MNP connection if possible, else disconnect 5 - Establish an MNP connection if possible, else Direct Connection. 7 - Establish an MNP connection if possible, else Normal connection | 7 | Negotiation Failure Treatment
`S37` | 1 = 300 bps 5 = 1200 bps 6 = 2400 bps 7 = 1200/75 bps (v.23 mode) 8 = 4800 bps 9 = 9600 bps 10 = 12000 bps 11 = 14400 bps 12 = 7200 bps | 0 | Negotiation Speed (Intial handshake)

Many modems have dozens, even hundreds, of S registers, but only the first dozen or so are fairly standard. They are changed with a command like ATS`n`=`N`, and examined with ATS`n`? (e.g. `AT S10`=70` S1?` would tell the modem not to hang up for seven seconds should it not hear the answering modem, and return the number of times the phone last rang.)

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