MX COM Inc MX860D1, MX860D6 Datasheet

COMMUNICATION SEMICONDUCTORS

CMX860

DATA BULLETIN

Telephone Signaling

Transceiver

¤¤¤¤2000 MX-COM, Inc. www.mxcom.com tel: [phone] 744 5050 fax: [phone] Doc. # 20480222.001

4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA All trademarks and service marks are held by their respective companies.

ADVANCE INFORMATION

Features Applications

• V.23 1200/75bps FSK Transmit and Receive

• DTMF/Tones Transmit and Receive

• Line & Telephone Complementary Drivers

• Call Progress Decoder

• CAS Tones Detection and Generation

• Simple ‘C-BUS’ Serial Interface

• Low Power Operation

• ‘Powersave’ Standby Mode

• Least Cost Routers

• Vending Machines

• Alarm Systems

• Home Management Systems

• Remote Meter Reading

• Internet Appliance Applications

• Cable TV Set-Top Boxes

• Advanced Feature Phones

'C-BUS'
SERIAL

INTERFACE

PHONE

LINE

CMX860

PHONE

INTERFACE

LINE

INTERFACE

HOST

µC

TX USART / FSK MODULATOR
& TONE / DTMF GENERATOR

RX USART / FSK RECEIVER
CALL PROGRESS, CAS &
ANSWER TONE DETECTOR
DTMF DECODER

RING DETECTOR

HOOK DETECTOR

RELAY DRIVER

The CMX860 is a flexible, low power Telephone Signaling Transceiver IC designed for use in a wide range of
line-powered telephone equipment.

The IC combines the functions of a DTMF encoder and decoder, V.23 modulator and demodulator plus call
progression circuitry with analog switching between line and phone interfaces. Ring detection, local phone off­hook detection, and a relay for line hook-switch operation are also provided under the control of C-BUS. The
ring and hook detectors operate while the remainder of the IC is powersaved, generating an interrupt to wake­up the host

µC when further processing or signaling is required.

All on-chip functions and switching arrangements are controlled via a serial bus (C-BUS). The CMX860 is
designed to operate at 2.7V and utilizes MX-COM’s low power DTMF decoder and V.23 modem technology.
The CMX860 is available in 28-pin SSOP (CMX860D6) and 28-pin SOIC (CMX860D1) packages.

Telephone Signaling Transceiver 2 CMX860 Advance Information

¤¤¤¤2000 MX-COM, Inc. www.mxcom.com tel: [phone] 744 5050 fax: [phone] Doc. # 20480222.001

4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA All trademarks and service marks are held by their respective companies.

CONTENTS

Section Page

1. Block Diagram............................................................................................................... 4

2. Signal List...................................................................................................................... 5

3. External Components ................................................................................................... 7

3.1 Ring Detector Interface.........................................................................................................9

3.2 Hook Detector Interface...................................................................................................... 10

3.3 Line Interface...................................................................................................................... 10

3.4 Phone Interface .................................................................................................................. 10

4. General Description .................................................................................................... 11

4.1 Tx USART ..........................................................................................................................11

4.2 FSK Modulator.................................................................................................................... 12

4.3 Tx Filter and Equalizer........................................................................................................ 12

4.4 DTMF/Tones Generator...................................................................................................... 12

4.5 Tx Level Control and Output Buffers ................................................................................... 12

4.6 DTMF Decoder and Tone Detectors ................................................................................... 12

4.7 Rx Modem Filter and Equalizer........................................................................................... 13

4.8 FSK Demodulator ............................................................................................................... 13

4.9 Rx Data Register and USART............................................................................................. 14

4.10 Rx Modem Pattern Detectors (and Descrambler)............................................................. 14

4.11 Analog Signal Routing ..................................................................................................... 15

4.12 C-BUS Interface............................................................................................................... 15

4.12.1 General Reset Command (no data) ($01) ............................................................................ 16

4.12.2 General Control Register: 16-bit write-only ($E0)................................................................. 17

4.12.3 Transmit Mode Register: 16-bit write-only ($E1) .................................................................. 18

4.12.4 Receive Mode Register: 16-bit write-only ($E2) ................................................................... 20

4.12.5 Tx Data Register: 8-bit write-only ($E3) ............................................................................... 21

4.12.6 Rx Data Register: 8-bit read-only ($E5) ............................................................................... 21

4.12.7 Analog Signal Path Register: 8-bit write-only ($EC)............................................................. 22

4.12.8 Status Register: 16-bit read-only ($E6) ................................................................................ 23

4.12.9 Programming Register

(includes generation & detection of CAS): 16-bit write-only ($E8) ....................................... 26

4.12.10 Other Registers..................................................................................................................... 28

Telephone Signaling Transceiver 3 CMX860 Advance Information

¤¤¤¤2000 MX-COM, Inc. www.mxcom.com tel: [phone] 744 5050 fax: [phone] Doc. # 20480222.001

4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA All trademarks and service marks are held by their respective companies.

5. Application Notes........................................................................................................ 29

6. Performance Specification......................................................................................... 30

6.1 Electrical Performance........................................................................................................ 30

6.1.1 Absolute Maximum Ratings .................................................................................................. 30

6.1.2 Operating Limits.................................................................................................................... 30

6.1.3 Operating Characteristics ..................................................................................................... 31

6.1.4 Timing ................................................................................................................................... 35

6.2 Packages............................................................................................................................ 35

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

Telephone Signaling Transceiver 4 CMX860 Advance Information

¤¤¤¤2000 MX-COM, Inc. www.mxcom.com tel: [phone] 744 5050 fax: [phone] Doc. # 20480222.001

4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA All trademarks and service marks are held by their respective companies.

1. Block Diagram

CALL PROGRESS DECODER

DTMF DECODER

V.23 FSK DECODER

CAS DETECTOR

ANSWER TONE DETECTOR

DTMF/TONES GENERATOR

V.23 FSK GENERATOR

'C-BUS'

SERIAL

INTERFACE

SERIAL CLOCK

COMMAND DATA

REPLY DATA

CS

IRQ

V

BI AS

LINE

CONNECTION

PHONE

CONNECTION

RING

DETECT

OFF-HOOK

DETECT

XTAL

RDRV

XTAL/

CLOCK

RESET

DV

SS

AV

SS

DV

DD

AV

DD

EN

EN

LINE

RXAMPOUT

LINERX-

LINERX+

LINETX+

LINETX-

PHONE

RXAMPOUT

PHONERX-

PHONERX+

PHONETX+

PHONETX-

RT

RD

HT

HD

+

-

-

+

-

+

-

+

Figure 1: Block Diagram

Telephone Signaling Transceiver 5 CMX860 Advance Information

¤¤¤¤2000 MX-COM, Inc. www.mxcom.com tel: [phone] 744 5050 fax: [phone] Doc. # 20480222.001

4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA All trademarks and service marks are held by their respective companies.

2. Signal List

CMX860

D6, D1

Signal

Pin No. Name Type

Description

1

XTAL

output The output of the on-chip Xtal oscillator inverter.

2 XTAL/CLOCK input The input to the oscillator inverter from the Xtal circuit or

external clock source.

3

RDRV

output Relay drive output, low resistance pull down to DV

SS

when active and medium resistance pull up to DV

DD

when inactive.

4 DVSS Power The digital negative supply rail (ground).

5 RD input Schmitt trigger input to the Ring signal detector. Connect

to DV

SS

if Ring Detector not used.

6 RT bi-directional Open drain output and Schmitt trigger input forming part

of the Ring signal detector. Connect to DV

DD

if Ring

Detector not used.

7

RESET

input An active-low reset pin. Can be used as part of a power-

up reset function.

8 LINE

RXAMPOUT

output The output of the Phone Rx Input Amplifier.

9 LINERX- input The inverting input to the Phone Rx Input Amplifier.

10 LINERX+ input The non-inverting input to the Phone Rx Input Amplifier.

11 PHONE

RXAMPOUT

output The output of the Line Rx Input Amplifier.

12 PHONERX- input The inverting input to the Line Rx Input Amplifier.

13 PHONERX+ input The non-inverting input to the Line Rx Input Amplifier.

14 AVSS Power The analog negative supply rail (ground).

15 V

BIAS

output Internally generated bias voltage of approximately

AV

DD

/2, except when the device is in ‘Powersave’ mode

when V

BIAS

will discharge to AVSS. Should be decoupled

to AV

SS

by a capacitor mounted close to the device pins.

16 PHONETX- output The inverted output of the Phone Tx Output Buffer.

17 PHONETX+ output The non-inverted output of the Phone Tx Output Buffer.

18 LINETX- output The inverted output of the Line Tx Output Buffer.

19 LINETX+ output The non-inverted output of the Line Tx Output Buffer.

20 AVDD Power The analog positive supply rail. Levels and thresholds

within the device are proportional to this voltage.

21 HT bi-directional Open drain output and Schmitt trigger input forming part

of the Hook signal detector. Connect to DV

DD

if Hook

Detector not used.

22 HD input Schmitt trigger input to the Hook signal detector.

Connect to DV

SS

if Hook Detector not used.

23

CS

input

The C-BUS chip select input from the

µC.

24 COMMAND DATA input

The C-BUS serial data input from the

µC.

25 SERIAL CLOCK input

The C-BUS serial clock input from the

µC.

Telephone Signaling Transceiver 6 CMX860 Advance Information

¤¤¤¤2000 MX-COM, Inc. www.mxcom.com tel: [phone] 744 5050 fax: [phone] Doc. # 20480222.001

4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA All trademarks and service marks are held by their respective companies.

26 REPLY DATA tri-state

A 3-state C-BUS serial data output to the

µC. This output

is high impedance when not sending data to the

µC.

27

IRQ

output

A ‘wire-ORable’ output for connection to a

µC Interrupt

Request input. This output is pulled-down to DV

SS

when
active and is high impedance when inactive. An external
pull-up resistor is required i.e. R1 of Figure 2.

28 DVDD Power The digital positive supply rail. Levels and thresholds

within the device are proportional to this voltage.

The J5 package is only available as samples.

Table 1: Signal List

Telephone Signaling Transceiver 7 CMX860 Advance Information

¤¤¤¤2000 MX-COM, Inc. www.mxcom.com tel: [phone] 744 5050 fax: [phone] Doc. # 20480222.001

4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA All trademarks and service marks are held by their respective companies.

3. External Components

CMX860

D6/D1

1

C1

C2

C3

X1

XTAL

XTAL/CLOCK

'C-BUS'

to/from

µC

Ring

Detector

Hook

Detector

Phone

Interface

Line

Interface

Phone

Interface

Line

Interface

SERIAL CLOCK
COMMAND DATA

REPLY DATA

CS
HD
HT

IRQ

RDRV

RT

RESET

LINERXAMPOUT

LINERX+

LINERX-

PHONETX+

LINETX+

PHONERX-

PHONERXAMPOUT

PHONERX+

PHONETX-

LINETX-

RD

DV

DD

AV

SS

AV

SS

AV

SS

DV

SS

V

BI AS

2

5
6

8

9
10
11

7

12
13
14 15

16

17

18

19

20

21

22

23

24

25

26

27

28

R1

DV

DD

DV

DD

DV

SS

3

4

AV

DD

C6

C7

+

AV

DD

AV

SS

AV

SS

C4

C5

+

DV

DD

DV

SS

DV

SS

Figure 2: Recommended External Components for a Typical Application

R1

100k

Ω

C1, C2 22pF

X1 11.0592MHz C3, C4 100nF

or 12.288MHz C5 10uF

Resistors ±5%, capacitors ±20% unless otherwise stated.

Table 2: Recommended External Components for a Typical Application

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

DD,

AV

DD,

and

V

BIAS

should be decoupled and the receive path protected from extraneous in-band signals. It is

recommended that the printed circuit board be laid out with both AV

SS

and DVSS ground planes in the
CMX860 area, as shown in Figure 3, with provision to make a link between them close to the CMX860. To
provide a low impedance connection to ground, the decoupling capacitors (C3-C7) must be mounted as close
to the CMX860 as possible and connected directly to their respective ground plane. This will be achieved
more easily by using surface mounted capacitors.

V

BIAS

is used as an internal reference for detecting and generating the various analog signals. It must be
carefully decoupled, to ensure its integrity. Apart from the decoupling capacitor shown (C3), no other loads
are allowed. If V

BIAS

needs to be used to set external analog levels, it must be buffered with a high input

impedance buffer. The DV

SS

connections to the Xtal oscillator capacitors C1 and C2 should also be of low

impedance and preferably be part of the DV

SS

ground plane to ensure reliable start up of the oscillator.

Telephone Signaling Transceiver 8 CMX860 Advance Information

¤¤¤¤2000 MX-COM, Inc. www.mxcom.com tel: [phone] 744 5050 fax: [phone] Doc. # 20480222.001

4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA All trademarks and service marks are held by their respective companies.

CMX860

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

AV

SS

AV

SS

V

BI AS

DV

SS

Provision

for a

Wire Link

DV

SS

DV

DD

C3

C7

L2

L1

C6

C5

C4

DV

DD

AV

DD

AV

DD

+

+

Figure 3: Recommended Power Supply Connections and De-coupling

ANALOG DIGITAL

C3, C6 100nF C4 100nF

C7

10

µF

C5

10µF

L2 100nH L1 100nH

Note: Inductors L1 and L2 can be omitted but this may degrade system performance.

Table 3: Recommended Power Supply Connections and De-coupling

Telephone Signaling Transceiver 9 CMX860 Advance Information

¤¤¤¤2000 MX-COM, Inc. www.mxcom.com tel: [phone] 744 5050 fax: [phone] Doc. # 20480222.001

4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA All trademarks and service marks are held by their respective companies.

3.1 Ring Detector Interface

Figure 4 shows how the CMX860 may be used to detect the large amplitude ringing signal voltage present on
the 2-wire line at the start of an incoming telephone call.

The ring signal is usually applied at the subscriber's exchange as an ac voltage inserted in series with one of
the telephone wires and will pass through either C20 and R20 or C21 and R21 to appear at the top end of
R22 (point X in Figure 4) in a rectified and attenuated form.

The signal at point X is further attenuated by the potential divider formed by R22 and R23 before being
applied to the CMX860 RD input. If the amplitude of the signal appearing at RD is greater than the input
threshold (Vt

HI

) of Schmitt trigger 'A' then the N transistor connected to RT will be turned on, pulling the

voltage at RT to DV

SS

by discharging the external capacitor C22. The output of the Schmitt trigger 'B' will then

go high, setting bit 14 (Ring Detect) of the Status Register.

The minimum amplitude ringing signal that is certain to be detected is:

( 0.7 + Vt

HI

x [R20 + R22 + R23] / R23 ) x 0.707V

RMS

where Vt

HI

is the high-going threshold voltage of the Schmitt trigger A (see Section 6.1).

With R20-22 all 470k

Ω as Figure 4, then setting R23 to 68kΩ will guarantee detection of ringing signals of

40Vrms and above for DV

DD

over the range 3V to 5V.

2-Wire

Telephone

Line

RD

CMX860

To Status

Register

RT

DV

DD

DV

SS

DV

SS

D1 - 4

C20

C22

R20

R21

R22

R23

R24

C21

RT

Status Register bit 14
(Ring Detect)

Bridge rectifier output (X)

Ring signal

Vt

HI

DV

SS

DV

SS

Vt

HI

A

B

X

Figure 4: Ring Signal Detector Interface Circuit

R20, 21, 22

470k

Ω

C20, 21

0.1µF

R23 See text C22

0.33

µF

R24

470k

Ω

D1-4 1N4004

Resistors ±5%, capacitors ±20%, unless otherwise stated

If the time constant of R24 and C22 is large enough then the voltage on RT will remain below the threshold of
the 'B' Schmitt trigger for the duration of a ring cycle.

The time for the voltage on RT to charge from DV

SS

towards DVDD can be derived from the formula:

V

RT

= DV

DD

x [1 - exp(-t/(R24 x C22)) ]

As the Schmitt trigger high-going input threshold voltage (Vt

HI

) has a minimum value of 0.56 x DVDD, then the

Schmitt trigger B output will remain high for a time of at least 0.821 x R24 x C22 following a pulse at RD.

Telephone Signaling Transceiver 10 CMX860 Advance Information

¤¤¤¤2000 MX-COM, Inc. www.mxcom.com tel: [phone] 744 5050 fax: [phone] Doc. # 20480222.001

4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA All trademarks and service marks are held by their respective companies.

The values of R24 and C22 given in Figure 4 (470kΩ and 0.33µF) give a minimum RT charge time of 100ms,

which is adequate for ring frequencies of 10Hz or above.

Note, that the circuit will also respond to a telephone line voltage reversal. If necessary, the

µC can

distinguish between a Ring signal and a line voltage reversal by measuring the time that bit 14 of the Status
Register (Ring Detect) is high.

If the Ring detect function is not used then pin RD should be connected to DV

SS

and RT to DV

DD

.

3.2 Hook Detector Interface

This is identical internally to the Ring Detector interface circuit and similar components could be used
externally, with appropriate values, if hook detection is to be performed by detecting a voltage change across
the tip and ring lines to the local phone.

3.3 Line Interface

Figure 5: 2-Wire Line Interface Circuit: Application Circuits are TBD

3.4 Phone Interface

Figure 6: 2-Wire Phone Interface Circuit: Application Circuits are TBD

Telephone Signaling Transceiver 11 CMX860 Advance Information

¤¤¤¤2000 MX-COM, Inc. www.mxcom.com tel: [phone] 744 5050 fax: [phone] Doc. # 20480222.001

4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA All trademarks and service marks are held by their respective companies.

4. General Description

The CMX860 transmit and receive operating modes are independently programmable.

The transmit mode can be set to any one of the following:

• V.23 modem. 1200 or 75bps FSK.

• DTMF transmit.

• Single tone transmit (from a range of modem calling, answer and other tone frequencies)

• User programmed tone or tone pair transmit (programmable frequencies and levels)

• Disabled.

The receive mode can be set to any one of the following:

• V.23 modem. 1200 or 75bps FSK.

• DTMF decode.

• 2100Hz and 2225Hz answer tone detect.

• Call progress signal detect.

• User programmed tone or tone pair detect.

• Disabled.

The CMX860 may also be set into a Powersave mode that disables all circuitry except for the C-BUS
interface, the Ring Detector and the Hook Detector.

4.1 Tx USART

A flexible Tx USART is provided. It can be programmed to transmit continuous patterns, Start-Stop characters
or Synchronous Data.

In both Synchronous Data and Start-stop modes the data to be transmitted is written by the µC into the 8-bit
C-BUS Tx Data Register from which it is transferred to the Tx Data Buffer.

If Synchronous Data mode has been selected the 8 data bits in the Tx Data Buffer are transmitted serially, b0
being sent first.

In Start-stop mode a single Start bit is transmitted, followed by 5, 6, 7 or 8 data bits from the Tx Data Buffer ­b0 first - followed by an optional Parity bit then - normally - one or two Stop bits. The Start, Parity and Stop
bits are generated by the USART as determined by the Tx Mode Register settings and are not taken from the
Tx Data Register.

Tx Data Register

'C-BUS' Interface

Tx USART

Modem bit rate clock

Continuous

patterns

To FSK

Modulator

Tx data

from µC

Start/Stop

bits

Tx Data Buffer

Parity bit generator

USART Control

7 0

Figure 7: Tx USART