MX COM Inc MX614DW, MX614P, MX614TN Datasheet

COMMUNICATION SEMICONDUCTORS

MX614

DATA BULLETIN Bell 202 Compatible Modem

2000 MX-COM, INC. www.mxcom.com Tel: [phone] 744 5050 Fax: [phone] Doc. # 20480162.004

4800 Bethania Station Road, Winston-Salem, NC 27105 USA All Trademarks and Service Marks are held by their respective companies.

PRELIMINARY INFORMATION

Features Applications

• 1200bps - 1800bps half duplex Bell 202
Compatible Modem

• Optional 1200bps Data Retiming Facility
can eliminate external UART

• Optional 5bps and 150bps Back Channel

• Optional Line Equalization

• Low Voltage Operation (3.3V to 5.0V)

• Low Power Operation

1mA typ. @ 3.3V Operating Mode

1µµµµA typ. Zero-Power Mode

• Standard 3.58MHz Xtal/Clock

• Telephone Telemetry Applications

µC

Data

Control

Status

MX614

Line

Interface

Telephone

Line

The MX614 is a low voltage, low power CMOS integrated circuit designed for the reception or transmission of
asynchronous 1200bps data. This device is compatible with Bell 202 type systems. The MX614 supports
5bps and 150bps 'back channel' operation. Asynchronous data rates up to 1818bps are also supported.

The MX614 provides an optional Tx and Rx data retiming function which can eliminate, based on user
preference, the need for a UART in the associated µC when operating at 1200bps. An optional line equalizer
has been incorporated into the receive path and is controlled by an external logic level.

The MX614 may be used in a wide range of telephone telemetry systems. A very low current “Zero Power
Mode (1µA typ.) and an operating current of 1mA typ. @ V

DD

= 3.3V, make the MX614 ideal for portable,
terminal and line powered applications. A standard 3.58MHz Xtal/Clock is required and the device operates
from a 3.0V to 5.5V supply.

The MX614 is available in 24-pin TSSOP (MX614TN), 16-pin SOIC (MX614DW) and 16-pin PDIP (MX614P)
packages.

Bell 202 Compatible Modem 2 MX614 PRELIMINARY INFORMATION

2000 MX-COM, INC. www.mxcom.com Tel: [phone] 744 5050 Fax: [phone] Doc. # 20480162.004

4800 Bethania Station Road, Winston-Salem, NC 27105 USA All Trademarks and Service Marks are held by their respective companies.

CONTENTS

Section Page

1. Block Diagram................................................................................................................. 3

2. Signal List........................................................................................................................ 4

3. External Components ..................................................................................................... 5

4. General Description ........................................................................................................ 6

4.1 Xtal Osc and Clock Dividers....................................................................................................6

4.2 Mode Control Logic.................................................................................................................6

4.3 Rx Input Amplifier....................................................................................................................6

4.4 Receive Filter and Equalizer ...................................................................................................6

4.5 Energy Detector ......................................................................................................................7

4.6 FSK Demodulator....................................................................................................................7

4.7 FSK Modulator and Transmit Filter .........................................................................................8

4.8 Rx Data Retiming....................................................................................................................9

4.9 Tx Data Retiming ..................................................................................................................10

5. Application Notes.......................................................................................................... 12

5.1 Line Interface ........................................................................................................................12

6. Performance Specification........................................................................................... 13

6.1 Electrical Performance ..........................................................................................................13

6.2 Packaging .............................................................................................................................16

MX•COM, Inc. reserves the right to change specifications at any time and without notice.

Bell 202 Compatible Modem 3 MX614 PRELIMINARY INFORMATION

2000 MX-COM, INC. www.mxcom.com Tel: [phone] 744 5050 Fax: [phone] Doc. # 20480162.004

4800 Bethania Station Road, Winston-Salem, NC 27105 USA All Trademarks and Service Marks are held by their respective companies.

1. Block Diagram

TXD

M0

RXEQ

CLK

RXD

RDY

M1

DET

Energy
Detect

FSK

De-modulator

Receive
Filter and
Equalizer

Mode

Control

Logic

Rx/Tx Data

Re-timing

Transmit Filter

and Output Buffer

FSK

Modulator

RXIN

RXAMPOUT

TXOUT

Xtal Osc and

Clock Dividers

XTAL/

CLOCK

XTAL

V

DD

V

BIAS

V

BIAS

V

SS

Figure 1: Block Diagram

Bell 202 Compatible Modem 4 MX614 PRELIMINARY INFORMATION

2000 MX-COM, INC. www.mxcom.com Tel: [phone] 744 5050 Fax: [phone] Doc. # 20480162.004

4800 Bethania Station Road, Winston-Salem, NC 27105 USA All Trademarks and Service Marks are held by their respective companies.

2. Signal List

Pin No. Signal Description

P, DW TN Name Type

11

XTAL

output Output of the on-chip Xtal oscillator inverter.

2 2 XTAL/CLOCK input Input to the on-chip Xtal oscillator inverter.

3 5 M0 input A logic level input for setting the mode of the device. See

section 4.2

4 6 M1 input A logic level input for setting the mode of the device. See

section 4.2

5 7 RXIN input Input to the Rx input amplifier.

6 8 RXAMPOUT output Output of the Rx input amplifier

7 11 TXOUT output Output of the FSK generator.

812 VSSPower Negative supply (ground).

913 V

BIAS

output Internally generated bias voltage, held at VDD/2 when the

device is not in 'Zero-Power' mode. Should be bypassed to
V

SS

by a capacitor mounted close to the device pins.

10 14 RXEQ input A logic level input for enabling/disabling the equalizer in the

receive filter. See section 4.4

11 17 TXD input 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 4.9

12 18 CLK input A logic level input which may be used to clock data bits in or

out of the FSK Data Retiming block.

13 19 RXD output 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 4.8

14 20 DET output A logic level output of the on-chip Energy Detect circuit.

15 23

RDY

output "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 V

DD

.

16 24 V

DD

Power Positive supply. Levels and thresholds within the device are

proportional to this voltage. Should be bypassed to V

SS

by a

capacitor mounted close to the device pins.

3, 4,

9, 10,

15,
16,
21,

22

N/C No internal connection

Bell 202 Compatible Modem 5 MX614 PRELIMINARY INFORMATION

2000 MX-COM, INC. www.mxcom.com Tel: [phone] 744 5050 Fax: [phone] Doc. # 20480162.004

4800 Bethania Station Road, Winston-Salem, NC 27105 USA All Trademarks and Service Marks are held by their respective companies.

3. External Components

V

DD

V

BIAS

V

SS

MX614

16

15

14

13

12

11

10

98

7

6

5

4

3

2

1

DET

RDY

CLK

RXEQ

RXD

TXD

M1

TXOUT

RXAMPOUT

RXIN

M0

To / Fr o m µ C

From µC

C1

C2

C3

C4

X1

R1

XTAL/CLOCK

XTAL

V

DD

R1

100kΩ±5%

C1 C2 18pF

±10%

C3

0.1µF ±10%

C4

0.1µF ±10%

X1 Note 1 3.579545MHz

Figure 2: Recommended External Components for Typical Application

External Components Notes

1. IMPORTANT: 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 be placed so that connections between
them and the device pins are as short as practicable e.g. ≤ 1 inch from device pins. A ground plane
protecting the receive path will help attenuate interfering signals

2. A crystal frequency of 3.579545MHz ±0.1% is required for correct FSK operation. For best results, a
crystal oscillator design should drive the clock inverter input with signal levels of at least 40% of V

DD

peak-peak. Tuning fork crystals generally cannot meet this requirement. To obtain crystal oscillator
design assistance, consult your crystal manufacturer.

Bell 202 Compatible Modem 6 MX614 PRELIMINARY INFORMATION

2000 MX-COM, INC. www.mxcom.com Tel: [phone] 744 5050 Fax: [phone] Doc. # 20480162.004

4800 Bethania Station Road, Winston-Salem, NC 27105 USA All Trademarks and Service Marks are held by their respective companies.

4. General Description

4.1 Xtal Osc and Clock Dividers

Frequency and timing accuracy of the MX614 is determined by a 3.579545MHz clock signal 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 MX614 as well as generating undefined states of the RXD, DET and

RDY

outputs.

4.2 Mode Control Logic

The MX614's operating mode is determined by the logic levels applied to the M0 and M1 input pins:

M1 M0 Rx Mode Tx Mode

Data Retime

[1]

0 0 1200bps 150bps Rx

0 1 Off 1200bps Tx

1 0 1200bps Off / 5bps Rx

11 'Zero-Power' -

[1] If enabled

Note: On applying power to the device, the mode must be set to 'ZP', i.e. M0 = '1', M1 = '1', until V

DD

has stabilized.

In the 'Zero-Power' (ZP) mode, power is removed from all internal circuitry. When leaving the 'ZP' mode there
must be a delay of 20ms before any Tx data is passed to, or Rx data read from the device to allow the bias
level, filters, and oscillator to stabilize.

4.3 Rx Input Amplifier

This amplifier is used to adjust the received signal to the correct amplitude for the FSK receiver and Energy
Detect circuits (see section 5.1).

4.4 Receive Filter and Equalizer

The Receive Filter and Equalizer section is used to attenuate out of band noise and interfering signals,
especially the locally generated transmit tones which might otherwise reach the 1200bps FSK Demodulator
and Energy Detector circuits. This block also includes a switchable equalizer section. When the RXEQ pin is
low, the overall group delay of the receive filter is flat over the 1200bps frequency range. If the RXEQ pin is
high the receive filter's typical overall group delay will be as shown in Figure 3.