Consumer Microcircuits Limited FX604P3, FX604D4 Datasheet

CML Semiconductor Products

V23 Compatible Modem FX604

 1996 Consumer Microcircuits Limited

D/604/3 November 1996

Provisional Information

1.0 Features

•• 1200/75 bits/sec Full Duplex V23 compatible Modem with:

•• Optional 75bits/sec Back Channel •• Optional Line Equalisation

•• Optional 1200bits/sec Data

Retiming Facility

•• -40°C to +85°C Operating

Temperature

•• 3.58MHz Xtal/Clock Rate •• 16-pin SOIC and DIP Packages

•• 3.0 to 5.5V Supply; 1.0mA typ. at 3V

'Zero-Power' Mode; 1

µµA typ.

•• Conforms to relevant sections of

V23 and ETSI specifications

1.1 Brief Description

The FX604 is a low power CMOS integrated circuit for the reception or transmission of asynchronous
1200bits/sec data in accordance with CCITT V.23 and ETSI specifications. It is also capable of generating the
75bits/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. The device can disable the back channel or be operated so

only the mark or space tone is produced. An optional line equaliser is incorporated into the receive path, this is
controlled by an external logic level.

The FX604 may be used in a wide range of telephone telemetry systems. With a low voltage requirement of

3.0V it is suitable for both portable terminal and line powered applications. A very low current 'sleep' mode (1

µ

A typ.) and operating current of 1mA typ. mean the device is ideal for line powered applications. A 3.58MHz
standard Xtal/Clock rate is required and the device operates from a 3.0 to 5.5V supply. Both SOIC (D4) and
Plastic DIL (P3) 16-pin package types are available.

V.23 Compatible Modem FX604

 1996 Consumer Microcircuits Limited 2 D/604/3

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

V.23 Compatible Modem FX604

 1996 Consumer Microcircuits Limited 3 D/604/3

1.2 Block Diagram

Figure 1 Block Diagram

1.3 Signal List

FX604

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).

V.23 Compatible Modem FX604

 1996 Consumer Microcircuits Limited 4 D/604/3

FX604

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/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.

V.23 Compatible Modem FX604

 1996 Consumer Microcircuits Limited 5 D/604/3

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 FX604 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 FX604 as well as generating undefined states of the RXD, DET and RDYN outputs.