Low Power V.32 bis Modem
CMX869
6.10
Programming Register
Programming Register : 16-bit write-only.
C-BUS address $E8
This register is used to program the transmit and receive programmed tone pairs by writing appropriate
values to RAM locations within the CMX869. Note that these RAM locations are cleared by Powersave or
Reset.
The Programming Register should only be written to when the Programming Flag bit (b13) of the Status
Register is 1. The act of writing to the Programming Register clears the Programming Flag bit. When the
programming action has been completed (normally within 150µs) the CMX869 will set the bit back to 1.
When programming Transmit or Receive Tone Pairs, do not change the Transmit or Receive Mode
Registers until programming is complete and the Programming Flag bit has returned to 1.
Transmit Tone Pair Programming
4 transmit tone pairs (TA to TD) can be programmed.
The frequency (max 3.4kHz) and level must be entered for each tone to be used.
Single tones are programmed by setting both level and frequency values to zero for one of the pair.
Programming is done by writing a sequence of seventeen 16-bit words to the Programming Register. 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)
Word
Tone Pair
Value written
1
2
3
4
5
6
7
- - -
- - -
16
17
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
TA
TA
TA
TA
TB
TB
- - -
- - -
TD
TD
The Frequency values to be entered are calculated from the formula:
Value to be entered = desired frequency (Hz) * 3.414
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:
Value to be entered = desired Vrms * 93780 / AVDD
i.e. for 0.5Vrms at AVDD = 3.3V, the value to be entered is 14209 (3781 in Hex)
Programming a notone pair is done by writing zero to all four tone pair words. On power-up or after a
reset, the tone pairs TA-TC are set to notone, and TD is set to generate 2130Hz + 2750Hz at
approximately –18dBm (100mVrms) each. Unprogrammed tone pairs retain their previous values.
Allowance should be made for the transmit signal filtering in the CMX869 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.
© 2004 CML Microsystems Plc
35
D/869/4
CMLMICRO [ CML MICROCIRCUITS ]
