MX604 Просмотр технического описания (PDF) - MX-COM Inc

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MX604

v.23 Compatible Modem

MX-COM Inc  

v.23 Compatible Modem

7

MX604 PRELIMINARY INFORMATION

4.5 Energy Detector

The Energy Detector block operates by measuring the level of the signal at the output of the Receive Filter,

and comparing it against a preset threshold.

The DET output will be set high when the level has exceeded the threshold for a sufficient time. Amplitude

and time hysteresis are used to reduce chattering of the DET output in marginal conditions.

Note: This circuit may also respond to non-FSK signals such as speech.

Line Signal

DET

M0, M1

TeON

FSK signal

TeOFF

FSK Receive mode

See section 6.1 for definitions of TeON and TeOFF

Figure 4: FSK Level Detector Operation

4.6 FSK Demodulator

The FSK Demodulator block converts the 1200bps FSK input signal to a logic level received data signal which

is output via the RXD pin as long as the Data Retiming function is not enabled (see section 4.8). This output

does not depend on the state of the DET output.

When the Rx 1200bps mode is 'off' or in 'ZP' the DET and RXD pins are held low.

Note: In the absence of a valid FSK signal, the demodulator may falsely interpret speech or other extraneous

signals as data. For this reason it is advised that the RXD pin be read only when data is expected.

4.7 FSK Modulator and Transmit Filter

The FSK Modulator and Transmit Filter blocks produce a tone according to the TXD, M0 and M1 inputs as

shown in the table below, assuming data retiming is not being used:

M1

M0

TXD = 0

TXD = 1

1

1

-

1

0

0Hz[1]

0

0

450Hz

390Hz

0

1

2100Hz

1300Hz

FSK Modulator and Transmit Filter Note:

[1]

TXOUT held at approx. VDD/2.

When modulated at the appropriate baud rates, the Transmit Filter and associated external components (see

section 5.1) limit the FSK out of band energy sent to the line in accordance with Figure 5 and Figure 6,

assuming that the signal on the line is at -6dBm or less.

1998 MXCOM, INC.

Tele: 800 638 5577 336 744 5050 Fax: 336 744 5054

Doc. # 20480152.004

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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