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CMX605
(Rev.:2001)

Digital Line to POTS Interface

CML Microsystems Plc 

Digital Line to POTS Interface

CMX605

1.5 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 1.5.9.

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.

1.5.1 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.

1.5.2 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).

1.5.3 Tone/FSK Encoder and Tone Encoder

When bit 5 of the MODE Register is set to ‘1’ then these blocks generate FSK signals as determined by

bit 0 of the SETUP Register and the Tx data bits from the UART block, as shown in the table below:

SETUP Register

Bit 0

0

1

Tone/FSK Generator

V23 1200bps FSK

Bell 202 1200bps FSK

FSK Signal Frequency

‘0’ (Space)

2100Hz

2200Hz

FSK Signal Frequency

‘1’ (Mark)

1300Hz

1200Hz

When bit 5 of the MODE Register is set to ‘0’, these blocks generate single or dual tones from the range

shown in the tables on the following pages. Bit 6 of the MODE Register is then used to enable or disable

the block’s output to the Tx Signal Control, RING and TONEFSK outputs. There are four tone fields

addressed by bits 0 and 1 of the MODE Register.

© 2001 Consumer Microcircuits Limited

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D/605/6

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