DATA BULLETIN
MX375
Features
•
PRIVATE/CLEAR CAPABILITY
•
ON-CHIP TX AUDIO PRE/DEEMPHASIS
•
ALTERNATIVE TO STANDARD CTCSS
“PARTY LINE”
•
POWERSAVE OPTION
Pvt
SQUELCH
TM
CTCSS
Encoder/Decoder
Applications
•
MOBILE RADIOS
•
COMMUNITY REPEATERS
•
TELEPHONE/RADIO INTERCONNECT
SYSTEMS
TX
TX Audio
Input
6dB/Octave
TX
Filter
Output
Balanced
Modulator
CLR
Input
-6dB/Octave
TX Audio Output
RX
BIAS
RX
RX Audio
Input
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
PTL
8-Bit
Shift
Register
and
Latches
LD5-LD0
Logic
Control
f
CARRIER
NoTone Output
f
CLK1
V
DD
f
CLK2
f
EMPH
RX Path
V
BIAS
TX Path
Private
V
SS
f
EMPH
f
CLK1
f
CARRIER
f
CLK2
f
EMPH
PVT
BIAS
TX
RX Audio Output
3333Hz
Reference
Hysteresis
Clocks
Filters
RX Tone Decoder Output
Decode Comparator Input
RX Tone Detect Output
CTCSS
Tone Detect
3333 Hz
TX Tone
Output
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.
PvtSQUELCH™
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
PvtSQUELCH
user groups (one per CTCSS tone) can share a single radio channel. With
PvtSQUELCH,
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).
© 1997 MX•COM Inc.
www.mxcom.com Tele: 800 638-5577 910 744-5050
Fax: 910 744-5054
Doc. # 20480026.007
4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA
All trademarks and service marks are held by their respective companies.
PvtSQUELCH
TM
CTCSS Encoder/Decoder
2
MX375
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.
© 1997 MX•COM Inc.
4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA
www.mxcom.com Tele: 800 638-5577 910 744-5050
All trademarks and service marks are held by their respective companies.
Fax: 910 744-5054
Doc. # 20480026.007
PvtSQUELCH
TM
CTCSS Encoder/Decoder
3
MX375
1. Block Diagram
Filter
Output
Balanced
Modulator
CLR
Input
-6dB/Octave
TX
TX Audio
Input
6dB/Octave
TX
TX Audio Output
RX
BIAS
RX
RX Audio
Input
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
PTL
8-Bit
Shift
Register
and
Latches
LD5-LD0
Logic
Control
f
CARRIER
NoTone Output
f
CLK1
V
DD
f
CLK2
f
EMPH
RX Path
V
BIAS
TX Path
Private
V
SS
f
EMPH
f
CLK1
f
CARRIER
f
CLK2
f
EMPH
PVT
BIAS
TX
RX Audio Output
3333Hz
Reference
Hysteresis
Clocks
Filters
RX Tone Decoder Output
Decode Comparator Input
RX Tone Detect Output
CTCSS
Tone Detect
3333 Hz
TX Tone
Output
Figure 1: Device Block Diagram
© 1997 MX•COM Inc.
4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA
www.mxcom.com Tele: 800 638-5577 910 744-5050
All trademarks and service marks are held by their respective companies.
Fax: 910 744-5054
Doc. # 20480026.007
PvtSQUELCH
TM
CTCSS Encoder/Decoder
4
MX375
2. Signal List
Pin No.
LH
1
2
3
4
J,P,LH8
28
1
2
3
V
DD
XTAL/CLOCK
XTAL
LOAD/
LATCH
power
input
output
input
5V supply pin.
This is the input to the clock oscillator inverter. An external 4 MHz Xtal or
clock input should be applied to this pin.
This is the 4 MHz output of the clock oscillator inverter.
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.
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”.
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).
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).
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.
The negative supply pin (ground).
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.
Name
Type
Description
8
10
RX TONE
DECODE
DECODE
COMPARATOR
output
9
11
input
10
12
RX TONE
DETECT
output
N/A
13
NOTONE
output
11
12
14
15
V
SS
TX TONE
OUTPUT
power
output
© 1997 MX•COM Inc.
4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA
www.mxcom.com Tele: 800 638-5577 910 744-5050
All trademarks and service marks are held by their respective companies.
Fax: 910 744-5054
Doc. # 20480026.007
PvtSQUELCH
TM
CTCSS Encoder/Decoder
5
MX375
Pin No.
LH
13
14
15
J,P,LH8
16
17
18
Name
V
BIAS
FILTER
OUTPUT
BALANCED
MODULATOR
INPUT
RX AUDIO
OUTPUT
TX AUDIO
OUTPUT
RX AUDIO
INPUT
TX AUDIO
INPUT
PTL
Type
Description
This pin is set internally to V
DD
/2. It must be externally decoupled using a
capacitor (C7) to V
SS
. See Figure 2.
output
input
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.
This is the input to the balanced modulator. Must be A.C. coupled to the
Filter Output via capacitor C4. See Figure 2.
Outputs the received audio from a buffered output stage and is held at
V
BIAS
when in TX.
Outputs the transmitted audio in TX. In RX, this pin is held at V
BIAS
.
The audio input for the RX mode. Input signals should be AC coupled via
external capacitor C6. See Figure 2
This is the TX Audio voice input. Signals should be AC coupled via
external capacitor C11. See Figure 2
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).
This input, together with Load/
Latch
, selects the operational mode of the
RX/ TX and
PrivateEnable
functions. See Table 5
16
17
18
19
20
19
20
21
22
23
output
output
input
input
input
21
22
23
24
25
26
CONTROL
input
RX/ TX
PRIVATE
ENABLE
RX TONE
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
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
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
© 1997 MX•COM Inc.
4800 Bethania Station Road, Winston-Salem, NC 27105-1201 USA
www.mxcom.com Tele: 800 638-5577 910 744-5050
All trademarks and service marks are held by their respective companies.
Fax: 910 744-5054
Doc. # 20480026.007
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