CMX865D2 CML Microcircuits, CMX865D2 Datasheet - Page 30

• Manufacturer Part Number: CMX865D2
• Description: FSK Modem and DTMF Codec
• Manufacturer: CML Microcircuits

FSK Modem and DTMF Codec
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 10a. 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.
Programming is done by writing a sequence of twenty-seven 16-bit words to the Programming Register.
The first word should be 32769 (8001 hex), the following twenty-six 16-bit words set the frequencies and
levels and are in the range 0 to 32767 (0000-7FFF hex).
© 2005 CML Microsystems Plc
Word
10
11
12
13
14
1
2
3
4
5
6
7
8
9
Value written
32769
Filter #1 coefficient b2 1
Filter #1 coefficient b1 1
Filter #1 coefficient b0 1
Filter #1 coefficient a2 1
Filter #1 coefficient a1 1
Filter #1 coefficient b2 2
Filter #1 coefficient b1 2
Filter #1 coefficient b0 2
Filter #1 coefficient a2 2
Filter #1 coefficient a1 2
Freq measurement #1 ncycles
Freq measurement #1 mintime
Freq measurement #1 maxtime
Figure 10a Programmable Tone Detectors
Figure 10b Filter Implementation
30
Word
15
16
17
18
19
20
21
22
23
24
25
26
27
Value written
Filter #2 coefficient b2 1
Filter #2 coefficient b1 1
Filter #2 coefficient b0 1
Filter #2 coefficient a2 1
Filter #2 coefficient a1 1
Filter #2 coefficient b2 2
Filter #2 coefficient b1 2
Filter #2 coefficient b0 2
Filter #2 coefficient a2 2
Filter #2 coefficient a1 2
Freq measurement #2 ncycles
Freq measurement #2 mintime
Freq measurement #2 maxtime
th
order IIR
CMX865
D/865/3