MC145442B 查看數據表（PDF） - Motorola => Freescale

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MC145442B

Single–Chip 300–Baud Modem

Motorola => Freescale 

GENERAL DESCRIPTION

The MC145442B and MC145443B are full–duplex low–

speed modems. They provide a 300–baud FSK signal for bi-

directional data transmission over the telephone network.

They can be operated in one of four basic configurations as

determined by the state of MODE (pin 13) and LB (pin 2).

The normal (non–loopback) and self test (loopback) modes

in both answer and originate modes will be discussed.

For an originate or channel 1 mode, a logic high level is

placed on MODE (pin 13) and a logic low level is placed on

LB (pin 2). In this mode, transmit data is input on TxD, where

it is converted to a FSK signal and routed through a low–

band band–pass filter. The filtered output signal is then buff-

ered by the Tx op–amp line driver, which is capable of driving

–9 dBm onto a 600 Ω line. The receive signal is connected

through a hybrid duplexer circuit on pins 15 and 16, RxA2

and RxA1. The signal then passes through the anti–aliasing

filter, the sample–and–hold circuit, is switched into the high–

band band–pass filter, and then switched into the ac amplifier

circuit. The output of the ac amplifier circuit is routed to the

demodulator circuit and demodulated. The resulting digital

data is then output through RxD (pin 5). The carrier detect

circuit receives its signal from the output of the ac amplifier

circuit and goes low when the incoming signal is detected

(see Figure 4a).

In the answer or channel 2 mode, a logic low level is

placed on MODE (pin 13) and on LB (pin 2). In this mode, the

data follows the same path except the FSK signal is routed to

the high–band band–pass filter and the sample–and–hold

signal is routed through the low–band band–pass filter (see

Figure 4b).

In the analog loopback originate or channel 1 mode, a logic

high level is placed on MODE (pin 13) and on LB (pin 2). This

mode is used for a self check of the modulator, demodulator,

and low–band pass–band filter circuit. The modulator side is

configured exactly like the originate mode above except the

line driver output (TxA, pin 17) is switched to the negative in-

put of the hybrid op–amp. The RxA2 input pin is open in this

mode and the non–inverting input of the hybrid circuit is con-

nected to VAG. The sample–and–hold output bypasses the

filter so that the demodulator receives the modulated Tx data

(see Figure 4c). This test checks all internal device compo-

nents except the high–band band–pass filter, which can be

checked in the answer or channel 2 mode test.

In the analog loopback or channel 2 mode, a logic low level

is placed on MODE (pin 13) and a logic high level on LB

(pin 2). This mode is used for a self check of the modulator,

demodulator, and high–band pass–band filter circuit. This

configuration is exactly like the originate loopback mode

above, except the signal is routed through the high–band

pass–band filter (see Figure 4d).

MC145442B•MC145443B

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MOTOROLA

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