MX COM Inc MX375J, MX375LH, MX375LH8, MX375P Datasheet

DATA BULLETIN

MX375

© 1997 MX•COM Inc. www.mxcom.com Tele: 800 638-5577 910 744-5050 Fax: [phone] Doc. # 20480026.007

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

Pvt

SQUELCHTM CTCSS

Encoder/Decoder

Features Applications

•

PRIVATE/CLEAR CAPABILITY

•

ON-CHIP TX AUDIO PRE/DEEMPHASIS

•

ALTERNATIVE TO STANDARD CTCSS
“PARTY LINE”

•

POWERSAVE OPTION

•

MOBILE RADIOS

•

COMMUNITY REPEATERS

•

TELEPHONE/RADIO INTERCONNECT
SYSTEMS

3333 Hz

CTCSS

T oneDetect

8-Bit
Shift

Register

and

Latches

Logic

TXTone

Output

V

V

V

DD

BIAS

SS

PTL

Private

TX Path

RX Path

f

f

f

f

EMPH

CLK2

CLK1

CARRIER

NoTone Output

Control

LD5-LD0

Reference

Hysteresis

RXTone Decoder Output

Decode Comparator Input

RXTone Detect Output

Clocks

3333Hz

XT AL

XT AL

RXTone Input
Load/Latch

D5 or Serial Enable 1
D4 or Serial Enable 2
D3 or Serial Data Input
D2 or Serial Clock Input

D1 Input
D0 Input

RX/TX
Control
Private Enable
Push-T o-Listen

BIAS

RX

TX

TX

PVT

CLR

f

f

f

f

f

EMPH

EMPH

CLK1

CARRIER

CLK2

TX Audio

Input

RX Audio

Input

Filter

Output

BIAS

RX

TX

RX Audio Output

TX Audio Output

Balanced
Modulator
Input

6dB/Octave

-6dB/Octave

Filters

The MX375 is a CMOS LSI microcircuit which combines CTCSS Encode/Decode operation with voice band frequency
inversion. Frequency inversion is achieved by modulating the input audio with a 3333 Hz carrier frequency. Higher voice
band frequencies are translated downward, and lower frequencies upward, resulting in a “mirror image” voice
transmission.

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SQUELCH



combines CTCSS with inverted speech to prevent users from understanding each other’s
communications unless the transmissions are accompanied by the group’s assigned tone. Its net effect is to eliminate
casual eavesdropping and give mobile radio users a certain degree of privacy at a minimal price. Up to 38

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SQUELCH

user groups (one per CTCSS tone) can share a single radio channel. With

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SQUELCH, competing businesses can

share a radio channel without compromising communications security.
Device features: 1) serial or parallel tone programming capability (serial or parallel offered on MX375J, P & LH8), 2) the

ability to operate under NOTONE conditions, 3) on-chip Tx and Rx audio filtering, 4) pin-selectable Private/Clear
operation, and 5) pre/deemphasis filters in the Tx path, for optimal recovered audio quality.

A low-cost 4 MHz crystal/clock and a single 5V supply are required for operation. The MX375 is available in the following
package styles: 28-pin PDIP (MX375P), 28-pin CDIP (MX375J) 28-pin PLCC (MX375LH8), and
24-pin PLCC (MX375LH).

Pvt

SQUELCHTM CTCSS Encoder/Decoder 2 MX375

© 1997 MX•COM Inc. www.mxcom.com Tele: 800 638-5577 910 744-5050 Fax: [phone] Doc. # 20480026.007

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.................................................................................................................................. 3

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

3. External Components...................................................................................................................... 6

4. General Description......................................................................................................................... 7

4.1.1 Pre- and De-emphasis.......................................................................................................................................7

4.1.2 Functions and Outputs.......................................................................................................................................7

5. Application ....................................................................................................................................... 8

5.1.1 CTCSS Programming........................................................................................................................................8

6. Performance Specification.............................................................................................................. 9

6.1 Electrical Performance.............................................................................................................................. 9

6.2 Timing Information ................................................................................................................................... 12

6.2.1 Serial Loading...................................................................................................................................................12

6.2.2 Parallel Loading................................................................................................................................................13

6.3 Packaging ................................................................................................................................................ 13

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

Pvt

SQUELCHTM CTCSS Encoder/Decoder 3 MX375

© 1997 MX•COM Inc. www.mxcom.com Tele: 800 638-5577 910 744-5050 Fax: [phone] Doc. # 20480026.007

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

1. Block Diagram

3333 Hz

CTCSS

Tone Detect

8-Bit
Shift

Register

and

Latches

Logic

TX Tone

Output

V

V
V

DD

BIAS

SS

PTL

Private

TX Path

RX Path

f

f

f

f

EMPH

CLK2

CLK1

CARRIER

NoTone Output

Control

LD5-LD0

Reference

Hysteresis

RX Tone Decoder Output

Decode Comparator Input

RX Tone Detect Output

Clocks

3333Hz

XTAL

XTAL

RX Tone Input
Load/Latch

D5 or Serial Enable 1
D4 or Serial Enable 2
D3 or Serial Data Input
D2 or Serial Clock Input

D1 Input
D0 Input

RX/TX
Control
Private Enable
Push-To-Listen

BIAS

RX

TX

TX

PVT

CLR

f

f

f

f

f

EMPH

EMPH

CLK1

CARRIER

CLK2

TX Audio

Input

RX Audio

Input

Filter

Output

BIAS

RX

TX

RX Audio Output

TX Audio Output

Balanced
Modulator
Input

6dB/Octave

-6dB/Octave

Filters

Figure 1: Device Block Diagram

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SQUELCHTM CTCSS Encoder/Decoder 4 MX375

© 1997 MX•COM Inc. www.mxcom.com Tele: 800 638-5577 910 744-5050 Fax: [phone] Doc. # 20480026.007

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

2. Signal List

Pin No. Name Type Description

LH J,P,LH8

128 VDDpower 5V supply pin.
2 1 XTAL/CLOCK input This is the input to the clock oscillator inverter. An external 4 MHz Xtal or

clock input should be applied to this pin.

32

XTAL

output This is the 4 MHz output of the clock oscillator inverter.

43

LOAD/

LATCH

input

This input controls the eight input latches: RX/

TX ,

PrivateEnable

, and

D0-D5, as detailed in Table 5. Alternatively, the RX/TX and

PrivateEnable

inputs can be addressed separately by setting the

Load/

Latch

and Control inputs as shown in Table 5. 1 MΩ pullup.

5-7 D4-D2 input

Programming Inputs (Serial Mode Only): These are the

RX/TX tone

programming and function inputs which enable the serial programming
mode. With Load/

Latch

at logic “0” serial data is loaded in the following

sequence: D5, D4, D3, D2, D1, D0, RX/

TX ,

PrivateEnable

. When these

8 bits have been clocked in on the rising clock edge, data is latched by
strobing the Load/

Latch

input “0 - 1 - 0” (See Figure 5).

Pin 5 (D4) =

Serial Enable2

Pin 6 (D3) = Serial Data Input
Pin 7 (D2) = Serial Clock Input

4-9 D5-D0 input

Parallel Programming Inputs: These are the RX/

TX tone programming

and function inputs which select the CTCSS tone (See Table 4).

For both Serial and Parallel Modes:

In RX, a NOTONE program enables
RX Audio Output and forces the RX Tone Decode Output to a logic “0”.
In TX, a NOTONE program generates a constant V

BIAS

-0.7V condition at

the TX Tone Output pin. Each input has a 1 MΩ pullup resistor.

810

RX TONE
DECODE

output The gated output of the decode comparator. In RX, a logic “0” indicates a

valid CTCSS tone decode condition, or the presence of NOTONE
programming. A logic “0” enables the RX audio path. In TX, this output is
held at logic “1”.

9 11 DECODE

COMPARATOR

input The voltage level at this pin is compared internally with a fixed reference

level. A greater input level compared to the reference will result in a logic
“0” at the RX Tone Decode output. This input should be externally
connected to the RX Tone Detect output via external integration
components C10, R2, R3, and D1 (see Figure 2).

10 12 RX TONE

DETECT

output In RX, this pin outputs a logical “1” when a valid programmed CTCSS

tone is received at the RX TONE INPUT. This input should be externally
connected to the Decode Comparator input via external integration
components C10, R2, R3, and D1 (see Figure 2).

N/A 13 NOTONE output This pin outputs a logic “0” when a Notone CTCSS code has been

programmed in RX. It is typically used to enable carrier squelch circuits
under Notone RX conditions.

11 14 V

SS

power The negative supply pin (ground).

12 15 TX TONE

OUTPUT

output The buffered CTCSS sinewave tone output appears on this pin. In TX

mode, the tone frequency is selected by program code (see Table 4); if
NOTONE is programmed, the output is at Vbias-0.7V. In RX mode, the
output goes open circuit. This is an emitter follower output with an
internal 10 kΩ load.

Pvt

SQUELCHTM CTCSS Encoder/Decoder 5 MX375

© 1997 MX•COM Inc. www.mxcom.com Tele: 800 638-5577 910 744-5050 Fax: [phone] Doc. # 20480026.007

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

Pin No. Name Type Description

LH J,P,LH8

13 16 V

BIAS

This pin is set internally to VDD/2. It must be externally decoupled using a
capacitor (C7) to V

SS

. See Figure 2.

14 17 FILTER

OUTPUT

output This is the output of the Input Audio Bandpass Filter. It must be A.C.

coupled to the Balanced Modulator Input via capacitor C4. See Figure 2.

15 18 BALANCED

MODULATOR

INPUT

input This is the input to the balanced modulator. Must be A.C. coupled to the

Filter Output via capacitor C4. See Figure 2.

16 19 RX AUDIO

OUTPUT

output Outputs the received audio from a buffered output stage and is held at

V

BIAS

when in TX.

17 20 TX AUDIO

OUTPUT

output Outputs the transmitted audio in TX. In RX, this pin is held at V

BIAS

.

18 21 RX AUDIO

INPUT

input The audio input for the RX mode. Input signals should be AC coupled via

external capacitor C6. See Figure 2

19 22 TX AUDIO

INPUT

input This is the TX Audio voice input. Signals should be AC coupled via

external capacitor C11. See Figure 2

20 23

PTL

input The “press to listen” function input. In RX mode, a logic “0” enables the

RX Audio Output directly, overriding tone squelch but not intercepting a
private conversation; in TX mode, a logic “0” reverses the phase of the TX
Tone Output for “squelch tail” reduction (see Table 5).

21 24 CONTROL

This input, together with Load/

Latch

, selects the operational mode of the

RX/

TX and

PrivateEnable

functions. See Table 5

22 25

RX/

TX

input This input selects the RX or TX mode (RX = 1, TX = 0). This can be

loaded in Serial or Parallel modes as described in Table 5

23 26

PRIVATE

ENABLE

This input selects either Private or Clear mode (Clear = 1, Private = 0),
and can be loaded by Serial or Parallel modes as described in Table 5.
This input has an internal 1 MΩ pullup resistor.

24 27 RX TONE

INPUT

input This is the received audio input to the on-chip CTCSS tone decoder. It

should be A.C. coupled via capacitor C5.

Note: The MX375LH package is available in serial mode only.

Table 1: Signal List