Consumer Microcircuits Limited FX614P3, FX614D4 Datasheet

CML Semiconductor Products

Bell 202 Compatible Modem FX614

 1997 Consumer Microcircuits Limited

D/614/4 October 1997

Advance Information

1.0 Features

•• 1200bits/sec 1/2 Duplex Bell 202 compatible Modem with:

•• Optional 5bits/sec and

150bits/sec Back Channel

•• Optional 1200bits/sec Data
Retiming Facility

•• 3.0 to 5.5V Supply; 1.0mA at 3V

'Zero-Power' Mode; 1

µµA

•• Optional Line Equalisation

•• -40°C to +85°C Operating

Temperature

•• 16-pin SOIC and DIL Packages

•• 3.58MHz Xtal/Clock Rate

1.1 Brief Description

The FX614 is a low power CMOS integrated circuit for the reception or transmission of asynchronous
1200bits/sec data and is suitable for use in Bell 202 type systems. It is also capable of generating the
5bits/sec or 150bits/sec 'back channel'.

The device incorporates an optional Tx and Rx data retiming function that removes the need for a UART in the
associated

µC when operating at 1200bits/sec. An optional line equaliser is incorporated into the receive path,

this is controlled by an external logic level.
The FX614 may be used in a wide range of telephone telemetry systems. With a low operating voltage of

3.0V, a very low current 'sleep' mode (1

µA) and an operating current of 1mA the device is ideal for portable,

terminal and line powered applications. A 3.58MHz standard Xtal/Clock rate is required and the device
operates from a 3.0V to 5.5V supply. Both SOIC (D4) and Plastic DIL (P3) 16-pin package types are available.

Bell 202 Compatible Modem FX614

 1997 Consumer Microcircuits Limited 2 D/614/4

CONTENTS

Section Page

1.0 Features ......................................................................................................1

1.1 Brief Description.........................................................................................1

1.2 Block Diagram ............................................................................................3

1.3 Signal List...................................................................................................3

1.4 External Components.................................................................................5

1.5 General Description....................................................................................5

1.5.1 Xtal Osc and Clock Dividers.......................................................5

1.5.2 Mode Control Logic ....................................................................6

1.5.3 Rx Input Amplifier.......................................................................6

1.5.4 Receive Filter and Equaliser.......................................................6

1.5.5 Energy Detector ..........................................................................7

1.5.6 FSK Demodulator ................................................................ ........7

1.5.7 FSK Modulator and Transmit Filter ................................ ............7

1.5.8 Rx Data Retiming ........................................................................9

1.5.9 Tx Data Retiming ................................................................ .......10

1.6 Application Notes.....................................................................................12

1.6.1 Line Interface.............................................................................12

1.7 Performance Specification.......................................................................13

1.7.1 Electrical Performance..............................................................13

1.7.2 Packaging..................................................................................16

Bell 202 Compatible Modem FX614

 1997 Consumer Microcircuits Limited 3 D/614/4

1.2 Block Diagram

Figure 1 Block Diagram

1.3 Signal List

FX614

D4/P3

Signal Description

Pin No. Name Type

1 XTALN O/P The output of the on-chip Xtal oscillator inverter.
2 XTAL/CLOCK I/P The input to the on-chip Xtal oscillator inverter.
3 M0 I/P A logic level input for setting the mode of the

device. See section 1.5.2.

4 M1 I/P A logic level input for setting the mode of the

device. See section 1.5.2.
5 RXIN I/P Input to the Rx input amplifier.
6 RXFB O/P Output of the Rx input amplifier, and the input to

the Rx filter.
7 TXOP O/P The output of the FSK generator.

8 V

SS

Power The negative supply rail (ground).

Bell 202 Compatible Modem FX614

 1997 Consumer Microcircuits Limited 4 D/614/4

FX614

D4/P3

Signal Description

Pin No. Name Type

9 V

BIAS

O/P Internally generated bias voltage, held at VDD/2

when the device is not in 'Zero-Power' mode.

Should be decoupled to VSS by a capacitor

mounted close to the device pins.

10 RXEQ I/P A logic level input for enabling/disabling the

equaliser in the receive filter. See section 1.5.4.

11 TXD I/P A logic level input for either the raw input to the

FSK Modulator or data to be re-timed depending

on the state of the M0, M1 and CLK inputs. See

section 1.5.9.

12 CLK I/P A logic level input which may be used to clock

data bits in or out of the FSK Data Retiming

block.

13 RXD O/P A logic level output carrying either the raw

output of the FSK Demodulator or re-timed

characters depending on the state of the M0, M1

and CLK inputs. See section 1.5.8.

14 DET O/P A logic level output of the on-chip Energy Detect

circuit.

15 RDYN O/P "Ready for data transfer" output of the on-chip

data retiming circuit. This open-drain active low

output may be used as an Interrupt

Request/Wake-up input to the associated

µC.

An external pull-up resistor should be connected

between this output and VDD.

16 V

DD

Power The positive supply rail. Levels and thresholds

within the device are proportional to this voltage.

Should be decoupled to VSS by a capacitor

mounted close to the device pins.

Notes: I/P = Input

O/P = Output

This device is capable of detecting and decoding small amplitude signals. To achieve this V

DD

and V

BIAS

decoupling and protecting the receive path from extraneous in-band signals are very important. It is
recommended that the decoupling capacitors are placed so that connections between them and the device
pins are as short as practicable. A ground plane protecting the receive path will help attenuate interfering
signals.

Bell 202 Compatible Modem FX614

 1997 Consumer Microcircuits Limited 5 D/614/4

1.4 External Components

R1

100k

Ω

C1, C2 18pF

X1 3.579545MHz C3

0.1

µF

C4

0.1

µF

Resistors

±5%, capacitors ±10% unless otherwise stated.

Figure 2 Recommended External Components for Typical Application

1.5 General Description

1.5.1 Xtal Osc and Clock Dividers

Frequency and timing accuracy of the FX614 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 supplied from
an external source, C1, C2 and X1 should not be fitted.

The on-chip oscillator is turned off in the 'Zero-Power' mode.
If the clock is provided by an external source which is not always running, then the 'Zero-Power' mode must be

set when the clock is not available. Failure to observe this rule may cause a significant rise in the supply
current drawn by FX614 as well as generating undefined states of the RXD, DET and RDYN outputs.