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
CMLMICRO [ CML MICROCIRCUITS ]
