Silicon Laboratories SI2493/57/34/15/04, SI2494/39 manual Registers, Register Descriptions, Ascii

AN93

5.6. S Registers

S registers are typically used to set modem configuration parameters during initialization and are not usually changed during normal modem operation. S-register values other than defaults must be written via the ATSn=x command after every reset event. S registers are specified as a decimal value (S1 for example), and the contents of the register are also decimal numbers. Table 45 lists the S registers available on the ISOmodem, their functions, default values, ranges of values, and units.

Many S registers are industry standards, such as S0 (number of rings for auto answer), S1 (ring count), and S2 (escape character) among others. However, there are usually variations in the function (and availability) of S registers from one chipset to another or from one chipset manufacturer to another. These variations are due to a combination of feature availability and choices made during the chip design. It is prudent to verify the compatibility of S-register functions, defaults, ranges, and values when adapting the ISOmodem to an existing design that uses another chipset. This simple step can save time and help speed product development. If a particular S register is not available on the ISOmodem, the register may not be necessary, or the function of the S register may be available with the use of U registers (discussed later) or through an AT command.

Table 45. S-Register Descriptions

Definition

S Register	Function	Default	Range	Units
(Decimal)		(Decimal)
0	Automatic answer—This value represents the number	0	0–255	rings
	of rings the ISOmodem must detect before answering
	a call. 0 disables auto answer.
1	Ring counter—Counts rings received on current call.	0	0–255	rings
2	ESC code character	43 (+)	0–255	(ASCII)
3	Carriage return character	13 (CR)	0–255	(ASCII)
4	Linefeed character	10 (LF)	0–255	(ASCII)
5	Backspace character	08 (BS)	0–255	(ASCII)
6	Dial tone wait timer—This timer sets the number of	02	0–255	seconds
	seconds the ISOmodem waits before blind dialing and
	is only active if blind dialing is enabled (X0, X1, X3).
7	Carrier wait timer—This timer starts when dialing is	80	0–255	seconds
	completed. It sets the number of seconds the modem
	waits without carrier before hanging up and the num-
	ber of seconds the modem waits for ringback when
	originating a call before hanging up. The register also
	sets the number of seconds the answer tone continues
	while using the AT*Y2A command.
8	Dial pause timer for “,” and “<” dial command modifiers	02	0–255	seconds
9	Carrier presence timer—Time the remote modem car-	06	1–255	0.1 second
	rier must be detected before activating or reactivating
	DCD (carrier loss debounce time).

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