CMX867 データシートの表示（PDF） - MX-COM Inc

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CMX867

Low Power V.22 Modem

MX-COM Inc  

Low Power V.22 Modem

11

CMX867 Advance Information

In all Synchronous Data modes data written to $E4 will be treated as though it had been written to $E3.

The underspeed transmission requirement of V.14 is automatically met by the CMX867. As in Start-Stop

mode it automatically inserts extra Stop bit(s) if it has to wait for new data to be loaded into the C-BUS Tx

Data Register.

The optional V.22 compatible data scrambler can be programmed to invert the next input bit in the event of 64

consecutive ones appearing at its input. It uses the generating polynomial:

1+ x −14 + x −17

4.2 FSK and DPSK Modulators

Serial data from the USART is fed via the optional scrambler to the FSK modulator if V.21, V.23, Bell 103 or

Bell 202 mode has been selected or to the DPSK modulator for V.22 and Bell 212A modes.

The FSK modulator generates one of two frequencies according to the transmit mode and the value of current

transmit data bit.

The DPSK modulator generates a carrier of 1200Hz (Low Band, Calling modem) or 2400Hz (High Band,

Answering modem) which is modulated at 600 symbols/sec as described below:

600bps V.22 signals are transmitted as a +90° carrier phase change for a ‘0’ bit, +270° for ‘1’.

For V.22 and Bell 212A 1200bps DPSK the transmit data stream is divided into groups of two consecutive bits

(dibits) which are encoded as a carrier phase change:

Dibit

(left-hand bit is the first of the pair)

00

01

11

10

Phase change

+90°

0°

+270°

+180°

4.3 Tx Filter and Equalizer

The FSK or DPSK modulator output signal is fed through the Transmit Filter and Equalizer block which limits

the out-of-band signal energy to acceptable limits. In 600 and 1200bps FSK and DPSK modes this block

includes a fixed compromise line equalizer which is automatically set for the particular modulation type and

frequency band being employed. This fixed compromise line equalizer may be enabled or disabled by bit 10

of the General Control Register. The amount of Tx equalization provided compensates for one quarter of the

relative amplitude and delay distortion of ETS Test Line 1 over the frequency band used.

4.4 DTMF/Tone Generator

In DTMF/Tones mode this block generates DTMF signals or single or dual frequency tones. In DPSK modem

modes, it is used to generate the optional 550 or 1800Hz guard tone.

4.5 Tx Level Control and Output Buffer

The outputs (if present) of the Transmit Filter and DTMF/Tone Generator are summed then passed through

the programmable Tx Level Control and Tx Output Buffer to the pins TXA and TXA . The Tx Output Buffer

has symmetrical outputs to provide sufficient line voltage swing at low values of VDD and to reduce harmonic

distortion of the signal.

4.6 Rx DTMF/Tones Detectors

In Rx Tones Detect mode the received signal, after passing through the Rx Gain Control block, is fed to the

DTMF / Tones / Call Progress / Answer Tone detector. The user may select any of four separate detectors:

The DTMF detector detects standard DTMF signals. A valid DTMF signal will set bit 5 of the Status Register

to 1 for as long as the signal is detected.

The programmable tone pair detector includes two separate tone detectors (see Figure 19). The first detector

will set bit 6 of the Status Register for as long as a valid signal is detected, the second detector sets bit 7, and

bit 10 of the Status Register will be set when both tones are detected.

2000 MX-COM, Inc.

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

Doc. # 20480219.001

4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA

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