Silicon Laboratories SI2493/57/34/15/04 - Manual (Page 103)

AN93
Rev. 1.3 103
5.7.8. U49–U4C (Ring Detect Registers)
U49, U4A, U4B, and U4C set a representation of the maximum ring frequency, the difference between the highest
and lowest valid ring frequency, minimum ring “on” time, and maximum ring cadence time (time on plus time off),
respectively. U49 is set as the hexadecimal equivalent of 2400 divided by the highest valid ring frequency in Hz.
U4A is set as the hexadecimal equivalent of 2400 divided by the minimum valid ring frequency in Hz minus 2400
divided by the maximum valid ring frequency in Hz.
U4B and U4C are set as the hexadecimal equivalents of the times in seconds multiplied by 2400. The default high
ring frequency, RGFH (U49), is 70.6 Hz. The default ring cadence minimum on time, RGMN, is 250 ms. The default
ring cadence maximum total time is 11 seconds.
5.7.9. U4D (Modem Control Register 1—MOD1)
U4D is a bit-mapped register that controls various telephony functions, including the enabling of calling and guard
tones and loop current verification prior to dialing. All bits in this register are read/write, except for bits, 15, 13, 9, 6,
2, and 0, which are reserved. These bits must not be written with a logic 1, and reading them returns a value of 0
(see Table 56).
Bit 14 (TOCT) = 0 (default) turns off the calling tone after answer tone detection and allows the calling-tone
cadence to complete before proceeding with the connect sequence (per V.25). TOCT = 1 turns off the calling tone
200 ms after answer-tone detection begins.
Bit 12 (NHFP) = 0 (default) disables hook-flash during pulse dialing (ignores & and ! dial modifiers). NHFP = 1
enables hook-flash during pulse dialing.
Bit 11 (NHFD) = 0 (default) disables hook-flash during dial string (tone or pulse). NHFD = 1 enables hook-flash
during (tone or pulse) dial string.
Bit 10 (CLPD) = 0 (default) Modem ignores loop current prior to dialing. If CLPD = 1, modem measures loop
current prior to dialing. This bit is used in conjunction with the loop-current debouncing registers, U50 and U51
(LCDN and LCDF), and U4D bit 1 (LLC). U50 provides a delay between the modem going off-hook and the loop
current measurement. The delay allows the loop current to stabilize prior to the measurement. Some countries
require the presence of loop current prior to dialing.
Bit 8 (FTP) = 0 (default) allows mixing tone and pulse dialing in a single AT command. FTP = 1 forces the first
dialing mode encountered (tone or pulse) for the entire AT command.
Bit 7 (SPDM) = 0 (default) causes the modem to pulse dial if an ATDP command is given. If this bit is set to 1 the
pulse dial modifier, P, is ignored, and the dial command is carried out as a tone dial (ATDT).
Bit 5 (GT18) = 0 (default) disables the 1800 Hz guard tone. GT18 = 1 enables the 1800 Hz guard tone.
Bit 4 (GT55) = 0 (default) disables the 550 Hz guard tone. GT55 = 1 enables the 550 Hz guard tone.
Bit 3 (CTE) = 0 (default) disables and CTE = 1 enables the calling tone referred to in bit 14 (TOCT). The calling
tone is a 1300 Hz tone in originate mode with a 0.5–0.7 sec on/1.5–2.0 sec off cadence as described in V.25.
Table 55. Ring Detect Registers
Register Name Description Default
U49 RGFH Ring frequency high (2400/maximum valid ring frequency in Hz). 0x0022
U4A RGFD Ring frequency delta (2400/minimum valid ring frequency in Hz) –
(2400/maximum valid ring frequency in Hz). 0x007A
U4B RGMN Ring cadence minimum “on” time in seconds multiplied by 2400. 0x0258
U4C RGNX Ring cadence maximum total time in seconds multiplied by 2400. 0x6720