CMX867D2 CML Microcircuits, CMX867D2 Datasheet - Page 31

• Manufacturer Part Number: CMX867D2
• Description: Low power V.22 modem
• Manufacturer: CML Microcircuits

Low Power V.22 Modem
Programming is done by writing a sequence of up to seventeen 16-bit words to the Programming
The first word should be 32768 (8000 hex), the following 16-bit words set the frequencies and levels and
are in the range 0 to 16383 (0-3FFF hex)
The Frequency values to be entered are calculated from the formula:
i.e. for 1kHz the value to be entered is 3414 (or 0D56 in Hex).
The Level values to be entered are calculated from the formula:
i.e. for 0.5Vrms at VDD = 3.0V, the value to be entered is 15630 (3D0E in Hex)
Note that allowance should be made for the transmit signal filtering in the CMX867 which attenuates the
output signal for frequencies above 2kHz by 0.25dB at 2.5kHz, by 1dB at 3kHz and by 2.2dB at 3.4kHz.
On powerup or after a reset, the tone pairs TA-TC are set to notone, and TD set to generate 2130Hz +
2750Hz at approximately –20dBm each.
Receive Tone Pair Programming
The programmable tone pair detector is implemented as shown in Figure 11a. The filters are 4
sections. The frequency detectors measure the time taken for a programmable number of complete input
signal cycles and compare this time against programmable upper and lower limits.
2001 Consumer Microcircuits Limited
Register.
Word
- - -
- - -
16
17
1
2
3
4
5
6
7
Tone Pair
- - -
- - -
TA
TA
TA
TA
TB
TB
TD
TD
Value to be entered = desired frequency (Hz) * 3.414
Value to be entered = desired Vrms * 93780 / V
Figure 11a Programmable Tone Detectors
Value written
32768
Tone 1 frequency
Tone 1 level
Tone 2 frequency
Tone 2 level
Tone 1 frequency
Tone 1 level
- - - - - - - - - -
- - - - - - - - - -
Tone 2 frequency
Tone 2 level
31
DD
th
order IIR
CMX867
D/867/2