ISDN TA POTS Interface

CMX625

 2001 Consumer Microcircuits Limited

17

D/625/2

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.

= 5.0V) are:

Single Tone

0dBm

Dual Tone (per tone)

-3dBm

DTMF High Frequency Tone

-3dBm

DTMF Low Frequency Tone

-5dBm

FSK Signal

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

Signal Level Adjustment

Bit 4

Bit 3

Bit 2

(dB)

0

0

0

0

0

0

1

-2

0

1

0

-4

0

1

1

-6

1

0

0

-8

1

0

1

-10

1

1

0

-12

1

1

1

-14

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

amplitude of

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

RING Signal Select

Bit 3

Bit 2

0

0

Square wave

0

1

Trapezoidal wave

1

0

Sinusoidal wave