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CMX605

Digital Line to POTS Interface

MX-COM Inc  

Digital Line to POTS Interface

3 External Components

Page 5 of 26

CMX605 Preliminary Information

C2

XTAL 1

X1 XTAL/CLOCK 2

16 VDD

15 RING

VDD

C4

C1

SERIAL CLOCK 3

14 AMPOUT

COMMAND DATA 4

13 IN-

REPLY DATA 5 CMX605 12 RXIN

VDD

CS 6

11 VBIAS

C3

R1

IRQ 7

10 SPM

VSS 8

9 TONEFSK

C5

Figure 2: Recommended External Components

R1

100k:

X1 3.579545 MHz

C1, C2

C3

C4, C5

18pF

0.1µF

1.0µF

Table 2: Recommended External Components

Recommended External Component Notes:

1. Resistors ±5%, capacitors ±10% unless otherwise stated.

2. For best results, a crystal oscillator design should drive the clock inverter input with signal levels of at least

40% of VDD, peak to peak. Tuning fork crystals generally cannot meet this requirement. To obtain crystal

oscillator design assistance, please consult your crystal manufacturer.

4 General Description

The CMX605 is a telecom tone generator and DTMF tone encoder/decoder. It has separate output ports for

the three different classes of signals encoded. These include Ringing signal, In-band tones or FSK data at

1200bps and High frequency metering pulses (SPM tones). It has a transmit level attenuator for In-band

tones or FSK data and an envelope control for SPM tones. It also has an uncommitted amplifier and uses the

industry standard 3.58MHz Xtal for its oscillator. These functions are controlled over a ‘C-BUS‘ serial µC

interface, which also carries the transmit FSK data and the DTMF decoded data.

The CMX605 should initially be reset by issuing a ‘C-BUS’ RESET command. Individual functions may be

disabled or enabled by the use of bits 5, 6 and 7 in the SETUP Register. See Section 4.9. Approximately

50ms should be allowed for the Tx dc level to settle at VBIAS before enabling the Tx functions (set bit 6 of the

MODE Register to ‘1’) after the CMX605 has been reset.

4.1 Xtal Osc and Clock Dividers

Frequency and timing accuracy of the CMX605 is determined by a 3.579545MHz clock present at the

XTAL/CLOCK pin. This may be generated by the on-chip oscillator inverter using the external components C1,

C2 and X1 of Figure 2, or may be supplied from an external source to the XTAL/CLOCK input. If the clock is

supplied from an external source, C1, C2 and X1 should not be fitted.

If the clock is provided by an external source which is not always running, then the CMX605 should be reset

when the clock is not available. Resetting the CMX605 will also turn off the on-chip oscillator. Failure to reset

the device may cause a rise in the supply current drawn by the CMX605.

4.2 Uncommitted Amplifier

This amplifier, with suitable external components, can be used either for adjusting the received signal to the

correct amplitude for the DTMF decoder or for adjusting the transmit signal level (for the line hybrid).

¤2001 MX-COM, Inc.

www.mxcom.com tel: 800 638 5577 336 744 5050 fax: 336 744 5054

Doc. # 20480195.005

4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA All trademarks and service marks are held by their respective companies.

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