MC145442DW Просмотр технического описания (PDF) - Motorola => Freescale

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производитель

MC145442DW

Single-Chip 300-Baud Modem

Motorola => Freescale 

3.579 MHz ± 0.1%

8

9

VDD

RTLA

20

Xout

TLA

17

Xin

11

TxD

TxA

15

RxA2

TEST

MC145442

600 Ω

MC145443

600 Ω

16 RxA1

RxD 5

TEST CDT

FB

OUTPUT 4

10

INPUT

0.1 µF

0.1 µF

Din

Dout

CCDT

CFB

Figure 1. AC Characteristics Evaluation Circuit

PIN DESCRIPTIONS

VDD

Positive Power Supply (Pin 6)

This pin is normally tied to 5.0 V.

VSS

Negative Power Supply (Pin 12)

This pin is normally tied to 0 V.

VAG

Analog Ground (Pin 19)

Analog ground is internally biased to (VDD – VSS) / 2. This

pin must be decoupled by a capacitor from VAG to VSS and a

capacitor from VAG to VDD. Analog ground is the common

bias line used in the switched capacitor filters, limiter, and

slicer in the demodulation circuitry.

TLA

Transmit Level Adjust (Pin 20)

This pin is used to adjust the transmit level. Transmit level

adjustment range is typically from – 12 dBm to – 9 dBm. (See

Applications Information.)

TxD

Transmit Data (Pin 11)

Binary information is input to the transmit data pin. Data

entered for transmission is modulated using FSK techniques.

A logic high input level represents a mark and a logic low rep-

resents a space (see Table 1).

TxA

Transmit Carrier (Pin 17)

This is the output of the line driver amplifier. The transmit

carrier is the digitally synthesized sine wave output of the

modulator derived from a crystal oscillator reference. When a

3.579 MHz crystal is used the frequency outputs shown in

Table 1 apply. (See Applications Information.)

Table 1. Bell 103 and CCITT V.21

Frequency Characteristics

Originate Mode

Answer Mode

Data

Transmit Receive Transmit Receive

Bell 103 (MC145443)

Space

1070 Hz 2025 Hz 2025 Hz 1070 Hz

Mark

1270 Hz 2225 Hz 2225 Hz 1270 Hz

CCITT V.21 (MC145442)

Space

1180 Hz 1850 Hz 1850 Hz 1180 Hz

Mark

980 Hz 1650 Hz 1850 Hz 980 Hz

NOTE: Actual frequencies may be ± 5 Hz assuming 3.579545 MHz

crystal is used.

MAXIMUM LEVEL OF OUT–OF–BAND ENERGY

RELATIVE TO THE TRANSMIT CARRIER LEVEL INTO 600 Ω (kHz)

0 2 3.4 4

16

64

256

0

– 20

– 25

15 dB/OCTAVE

– 55

– 60

Figure 2. Out–of–Band Energy

ExI

External Input (Pin 18)

The external input is the non–inverting input to the line

driver. It is provided to combine an auxiliary audio signal or

speech signal to the phone line using the line driver. This pin

should be connected to VAG if not used. The average level

must be the same as VAG to maintain proper operation. (See

Applications Information.)

DSI

Driver Summing Input (Pin 1)

The driver summing input may be used to connect an ex-

ternal signal, such as a DTMF dialer, to the phone line. A

series resistor, RDSI, is needed to define the voltage gain

AV (see Applications Information and Figure 6). When ap-

plying a signal to do DSI pin, the modulator should be

squelched by bringing SQT (Pin 14) to a logic high level. The

voltage gain, AV, is calculated by the formula AV = – Rf/RDSI

(where Rf ≈ 20 kΩ). For example, a 20 kΩ resistor for RDSI

will provide unity gain (AV = – 20 kΩ/20 kΩ = – 1). This pin

must be left open if not used.

RxD

Receive Data (Pin 6)

The receive data output pin presents the digital binary data

resulting from the demodulation of the receive carrier. If no

carrier is present, CD high, the receive data output (RxD) is

clamped high.

MC145442•MC145443

4

MOTOROLA

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