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CMX625

ISDN TA POTS Interface

CML Microsystems Plc 

ISDN TA POTS Interface

CMX625

1.5.10 SPM Generator

This block operates independently and has its own output pin. It can transmit 12kHz or 16kHz and is

controlled by bit 4 of the SETUP Register. Bit 7 of the MODE Register is used to enable or disable this

block. The signal has a rise and fall time each of about 4ms. The SPM signal rises from the bias level to

0dBm in 16 steps of ≈2dB magnitude, and falls from 0dBm to bias level in 16 steps of ≈2dB magnitude.

1.5.11 Transmit Signal Control

This block adjusts the amplitude of the FSK transmit signal output level, the level skew between DTMF

tones and the signal routing to the output ports.

Output signal levels are proportional to VDD. The nominal output signal levels (at 0dB attenuation and VDD

= 5.0V) are:

Single Tone

Dual Tone (per tone)

DTMF High Frequency Tone

DTMF Low Frequency Tone

FSK Signal

0dBm

-3dBm

-3dBm

-5dBm

0dBm

The level attenuator provides for level adjustment from 0dB to -14dB in -2dB steps. The typical level is

determined by bits 2 to 4 of the MODE Register as shown in the table below:

MODE Register

Bit 4 Bit 3 Bit 2

0

0

0

0

0

1

0

1

0

0

1

1

1

0

0

1

0

1

1

1

0

1

1

1

Signal Level Adjustment

(dB)

0

-2

-4

-6

-8

-10

-12

-14

The RING signal is a square, trapezoidal or sinusoidal wave. The square and trapezoidal wave have an

amplitude of ≈ VDD peak to peak and the sinusoidal wave has an amplitude of ≈ ½ VDD peak to peak. The

trapezoidal ringing waveform has a crest factor (CF) of 1.35. Bits 2 and 3 of the SETUP Register select

the waveform type as shown in the table below.

SETUP Register

Bit 3

Bit 2

0

0

0

1

1

0

RING Signal Select

Square wave

Trapezoidal wave

Sinusoidal wave

 2001 Consumer Microcircuits Limited

17

D/625/2

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