Specifications

AN93
Rev. 0.9 141
3.5.20.4. 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 100.
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.
3.5.20.5. Serbia and Montenegro Special Network
Requirements
The following are special network requirements for
Serbia and Montenegro. These specifications are based
on the best information available and are believed to be
correct. A complete specification was not available.
 DC Feed: 48 or 60 V
 Feeding Bridge: 2x400 Ω or 2x500 Ω
 Network Impedance: 600 Ω resistive
 On-Hook (Idle State) Noise: <–60 dBm
 On-Hook ac (Ringer) impedance: >2.5 kΩ
 DTMF Transmit: –9/–11 dBm and –6/–8 dBm are
allowed.
 Data Transmit Level: 0 dBm to –15 dBm in 1 dB
steps (average –13 dBmo)
 Out-of-band energy: Not specified
 Pulse Dial: 1.6/1 ±15% (Pulse/pause)
 Rep Rate: 10 pps
 Interdial Pause: 250 ms <x> 800 ms, ±10%
 Ring Tone: 25 Hz 80–90 V
eff

Dial Tone: 425 Hz ±15%
 Level: –8 dBm > x > –12 dBm
 Cadence: 200 ms ±10% ON
300 ms ±10% OFF
700 ms ±10% ON
800 ms ±10% OFF
 Busy Tone: 425 Hz ±15%
 Level: –8 dBm > x > –12 dBm
 Cadence: 500 ms ±10% ON
500 ms ±10% OFF
3.5.20.6. Country Parameters
The modem default settings are for the US-like
countries. Many countries use at least some of the
default register settings. Default values do not have to
be written when configuring the modem to operate in a
particular country, assuming the modem was reset just
prior to the configuration process.
To avoid confusion
and possible errors, the modem should be reset
prior to reconfiguration between countries.
Some countries have unusual requirements. For
example, registers U37–U40 set the number of pulses
to dial digits 0 through 9, respectively. By default, digit 1
has a setting of 1 pulse; digit 2 has a setting of 2 pulses,
and so on. Digit 0 has a setting of Ah (10 decimal)
pulses. This pulse arrangement is used nearly
universally throughout the world. However, there are
two exceptions: New Zealand and Sweden. New
Zealand requires ten pulses for 0, nine pulses for 1,
eight pulses for 2, and so on. Sweden, on the other
hand, requires one pulse for 0, two pulses for 1, and so
on.
Japan has a requirement for both the default 10 pps
pulse dialing and 20 pps pulse dialing. To configure the
modem for 20 pps, set U42 (PDBT) = 0x0022, U43
(PDMT) = 0x0010, and U45 (PDIT) = 0x0258. The %P
command may also be used.
The Netherlands has a unique dial tone filter. Other
countries, such as Japan, have special low-voltage loop
requirements. South Korea, Poland, and South Africa
have special ringer impedance requirements. Set all
country-specific parameters listed in the country
parameter table in "3.5.20.7. Country Parameters
Table".
If you want to use the +GCI command for a country and
modify one or more U-Registers, be sure to execute the
+GCI command first, then modify the desired
register(s). The +GCI command resets all U-Registers
through U86 and S7 to factory defaults before applying
the country-specific settings. Check with your
compliance laboratory to verify whether countries
accepting TBR21 still accept their previous settings. A
recent change to TBR21 drops the requirement for loop
current limiting. The settings listed in the table in
"3.5.20.7. Country Parameters Table" are configured to
enable current limiting. If you want to disable loop
current limiting, change the setting for U67(ILIM)[9] = 0b
after the +GCI command.
The table in "3.5.20.7. Country Parameters Table"
contains recommended updates to the +GCI register
settings. The U-Register writes must be loaded
after the
+GCI command. Some CTR/TBR 21 countries require
blacklisting. This can be enabled with S42 = 1. Some
also require a minimum period of time between calls
that can be set with S50 = 6.
Table 100. 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