# Serial Programming/Modems and AT Commands/S-Registers
## S-Registers
### S0: Ring to Answer After

Defines the number of ring bursts before the modem automatically answers an incoming call. When set to zero, auto-answer is disabled.

### S1: Ring Count

(Read only) Counts the number of ring bursts received. Reset to zero after 8 seconds of no ring.

### S2: Escape Sequence Character

Specifies the ASCII value of the character used in the escape code. (The escape code is the escape character entered three times in succession.) When the modem is in connect state and it receives the escape code, the modem enters command state. Setting register S2 to 128 or above disables the escape code character.

### S3: Carriage Return Character

Specifies the ASCII value of the carriage return (CR) character. The carriage return terminates command lines and result codes.

### S4: Line Feed Character

Specifies the ASCII value for the line feed (LF) character. The line feed character follows a carriage return at the end of long-form result codes. Short-form result codes are sent without line feeds.

### S5: Backspace Character

Specifies the ASCII value for the backspace (BS) character that you can use to edit the command line.

### S6: Wait Before Blind Dialing

Specifies the time the modem waits after going off-hook before it dials. This is a minimum of 2 seconds, even if register S6 is set to a value less than 2. Register S6 is used only when the X0, X1, or X3 command (Extended Result Codes) is set.

### S7: Wait for Carrier after Dialing

Specifies the time that the modem waits for one of the following before hanging up:
•Carrier from the remote modem when this modem is in originate or answer mode
•Ringback, only when this modem is in originate mode, and only if X3 or X4 (Extended Result Codes) is set
Register S7 is linked to register S37 so that the two registers share a single value. Changing the value of S7 changes the value of S37, and changing S37 changes S7.

### S8: Duration of Delay for Comma Dial Modifier

This register contains the pause time of the (,) dial modifier used in the dial string. Consecutive commas will invalidate the modem's approval if the total pause period exceeds 12 seconds.

### S9: Carrier Detect Response Time

This register contains the time period that a received carrier signal must be present for the modem to recognise it and turn on the DCD signal.

### S10: Delay Between Lost Carrier and Hang Up

Specifies the time the modem waits before hanging up after loss of carrier. This waiting period allows the modem to recover from a temporary loss of carrier without breaking the connection. Modems at both ends of the connection should have the same values set. If the S10 values of the two modems are unequal, disconnection occurs when the lower value is reached. When register S10 is set to 255, the modem functions as if carrier were always present; it never hangs up due to loss of carrier. After disconnecting in originate mode, the modem waits a minimum of 5 seconds before going off-hook.

### S11: DTMF Multi-Frequency Tone Duration

This register contains the time period of the duration and inter-digital pause of the DTMF dialling tones.