Silicon Laboratories SI2494/39 manual Country-Dependent Setup, DC Termination Control Bits

AN93

Table 88. Modem Feature vs. Hardware, AT Command and Register Setting (Continued)

Function/Feature	AT Commands	S Registers	U Registers
Quick connect	+PQC
	+PSS
Reset	Z		U6E [4], U70 [7,5]
SAS detect			U9F–UA9
Self Test	&Tn, &Hn	40, 41
SMS	+FCLASS
	+FRM
	+FTM
V.29	+FCLASS
	+FTM
	+FRM
V.42/V.42b	+DR, %Cn, \Nn,
	+DS
V.44*	+DS44, +DR
V.92	+MS
	+PIG
*Note: Si2493 only.

6.2. Country-Dependent Setup

Configuring the ISOmodem for operation in different countries is done easily with AT commands. In all but rare instances, no hardware change is required (the exceptions being an optional maximum ringer impedance, a billing- tone filter, etc.). For this reason, the ISOmodem is truly a global modem solution. Modem initialization commands for various countries are presented in "6.2.2.1. Country Initialization Table". All U-register values are in hexadecimal. The settings for different countries can be broken into three groups: call progress, dialing, and line- interface control. Call-progress settings include filter coefficients, cadence data, and threshold values. Dialing includes DTMF levels, thresholds, timing and pulse-dialing parameters. Line-interface settings include ac line impedance, off-hook voltage and current characteristics, ringer sensitivity, and transmit levels. CID (Caller ID) settings are discussed in a separate section. Tables 89–93 describe the registers and bits used for global configuration and the functions performed by each. Many countries use some or all of the default FCC settings.

6.2.1. DC Termination

The ISOmodem offers a great deal of flexibility in setting dc termination. Several bits can be used to adapt to particular country requirements and unusual line conditions. The dc termination control bits are shown in Table 89.

Table 89. DC Termination Control Bits

Reg	Bit	Val	Function
U67	7	DCR	DC Impedance Select
U67	3:2	DCV	DC Termination Select
U7D	10	LLV	Special low-voltage mode

A detailed description of each bit is given in the relevant U-register description section of this manual. The following discussion centers on the use of these bits alone or in combination to meet particular country requirements.

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