73M2901CE-IM/F 查看數據表（PDF） - Teridian Semiconductor Corporation

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73M2901CE-IM/F

V.22bis Single Chip Modem

Teridian Semiconductor Corporation 

DS_2901CE_031

73M2901CE Data Sheet

These commands are broken out as follows:

F

S99=1

Y0

Y6

K3

C1

C2

R2

S30=n

Bn

O2

S26+4

S70=12

@L1

Set to factor defaults

Set to U.S configuration (default)

Used clear channel mode (no speed buffering)

Use DTE/DCE speed buffering

Use RTS/CTS flow control

Use qualified carrier detection

Use raw carrier detection

Disconnect on DTR toggle

Set S30 to a modulation mode

Set to modulation mode

Respond to retrain requests

Enable auto retrain requests

Lower retrain request threshold to 12

Leased line mode

Once the initialization string is given, the modems are started by sending ATD to one modem and ATA to

the other. The modems will then begin sending carriers and look for carrier from the other modem. When

the modems disconnect using R2 and DTR, an “OK” result code is sent on RXD. The modem will stop

sending carrier at the end of the OK message, the delay time determined by the DTE speed and the time

it takes to output the message.

It is important to note the auto retrain feature (O2) should be enabled when using V.22bis. V.22bis

requires training when it connects and auto retrain is off by default. Make sure “S26+4” is also sent so it

can also initiate a retrain as well.

6.4.3 73M2901CE Energy Ring Detection

The 73M2901CE has a feature that was added with the intention of lowering the total modem cost by

eliminating some of the more expensive external components. The threshold for the ring detector

depends on the setting of the S123 register and the components in the Caller ID path, especially the

transformer. The number that S123 is set to represents the amplitude threshold of the ring signal (see

Table 2). In a conventional ring detect circuit the threshold is set by the hardware, usually the values of

the Zener diodes used in the ring detect circuit.

Table 3: Approximate Thresholds for Energy Ring Detection

Typical US Wet Transformer

S123 Register Setting with Frequency Checking 20 15 10

5

3

Vrms min off to on

45 34 24 12

7

Vrms min on to off

42 32 22 10

5

Typical ETSI TS 203 Dry Transformer Design

S123 Register Setting with Frequency Checking

20 15 10

5

3

Vrms min off to on

5

5

5

5

5

Vrms min on to off

5

5

5

5

5

Having the ability to set the threshold over a wide range through the S123 register eliminates the need to

change components to adjust the ring detection sensitivity. Energy ring detection uses the Caller ID path

and coupling transformer to path to pass the incoming ring signal to the modem so it can detect the ring

signal using the internal DSP. In an average design this can save at least $0.35 in the total parts cost or

even more in lower volume products. The 73M2901CE is still compatible with the earlier 2901 products

and still supports the opto-coupled ring detection method, although not on our current demo boards. Wet

transformers generally have poorer frequency response in the ring frequency range than dry

transformers. This means that the threshold must be sent to a lower number for wet transformers than

with some V.90-rated dry transformers. This also means that lower frequency ring signal detection will

also require a lower setting. The range of values for S123 can be from 1 to 127 when checking frequency

Rev. 3.4

17

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