Silicon Laboratories Si2404, Manual, Page: 95 / 307

AN93
Rev. 1.4 95
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 56 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 56. S-Register Descriptions
Definition
S Register
(Decimal)
Function Default
(Decimal)
Range Units
0 Automatic answer—This value represents the number
of rings the ISOmodem must detect before answering
a call. 0 disables auto answer. 0 0–255 rings
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
seconds the ISOmodem waits before blind dialing and
is only active if blind dialing is enabled (X0, X1, X3). 02 0–255 seconds
7 Carrier wait timer—This timer starts when dialing is
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. 80 0–255 seconds
8 Dial pause timer for “,” and “<” dial command modifiers 02 0–255 seconds
9 Carrier presence timer—Time the remote modem car-
rier must be detected before activating or reactivating
DCD (carrier loss debounce time). 06 1–255 0.1 second