PT260 Service Manual
5
Figure 3.4 MCU Unit Principle Diagram
MCU unit controls the operation of each unit of the radio so
as to realize all the functions.
Communicate with external PC.
Access the status data of the radio.
Control RDA1845 Rx and Tx.
Obtain the status of the current channel.
Control the status of LED indicator.
Control power supply of each unit.
Check the actions of each functional key.
Generate DCS signal.
Generate power control signal.
Perform CTCSS decoding.
Perform DCS decoding.
Test and control the squelch.
Control content of voice annunciation.
Memory (E
2
PROM, AT24C08)
The memory stores the channel data, CTCSS/DCS data, other
data for function setting and parameter adjusting data.
CTCSS/DCS Signal Encoding and Decoding
The CTCSS/DCS signal (output from pin 17, PWM wave)
generated by MCU passes through R624, R623, C616 and C617
filter and is sent to RDA 1845 for modulation.
The CTCSS/DCS signal from the receiver is sent to MCU for
modulation. The MCU will judge whether the CTCSS/DCS signal
in the receiver matches with the preset CTCSS/DCS signal of the
radio, and determines whether to turn on the speaker or not.
CTCSS
CTCSS（Continuous Tone Control Squelch System, CTCSSS
for short）is the squelch control system which is modulated on the
carrier, and uses the continuous sub-audio signal as the guide
frequency. If CTCSS is set, the communication between the
transmitting and receiving radios can be realized only when the two
radios have set the same CTCSS frequency. In doing this,
disturbance from other signals can be avoided.
This radio has 39 groups of standard CTCSS frequencies for
your selection (these CTCSS frequencies are compatible with any
of the CTCSS within 67-254.1Hz). See table 3.1.
The CTCSS signal (PWM wave) generated by MCU passes
through the low pass filter consisted of by RC to remove high
frequency components (above 300Hz). Then the resulting signal is
sent to VCO for modulation.
Table 3.1 CTCSS Frequency List
No. Frequency
[Hz]
No. Frequency
[Hz]
No. Frequency
[Hz]
No. Frequency
[Hz]
1 67.0 11 94.8 21 131.8 31 186.2
2 69.3 12 97.4 22 136.5 32 192.8
3 71.9 13 100.0 23 141.3 33 203.5
4 74.4 14 103.5 24 146.2 34 210.7
5 77.0 15 107.2 25 151.4 35 218.1
6 79.7 16 110.9 26 156.7 36 225.7
7 82.5 17 114.8 27 162.2 37 233.6
8 85.4 18 118.8 28 167.9 38 241.8
9 88.5 19 123.0 29 173.8 39 250.3
10 91.5 20 127.3 30 179.9
DCS
DCS (Digital Code Squelch), which is used to control
squelch, is a series of continuous digital codes modulated on the
carrier together with voice signal. If DCS is set, the speaker can
only be opened when the radio receives signal with the same DCS
to avoid disturbance of unwanted signals.
This radio has 83 standard codes (normal and inverse) for
your selection. See table 3.2.
DCS signal (PWM wave) is generated by MCU. It passes
through the low pass filter consisted of by RC to remove high
frequency components (above 300Hz), and then the processed
signal is sent to VCO and TCXO for modulation, with HF
components of the DCS signal being modulated by VCO, and the
LF components of the DCS signal being modulated by TCXO.
The DCS signal coming from the receiver is sent to MCU for
decoding. MCU checks if the DCS code in the received signal
matches the preset DCS of the radio, and determines whether to
open the speaker or not.
Table 3.2 DCS Codes
023 114 174 315 445 631
025 115 205 331 464 632
026 116 223 343 465 654
031 125 226 346 466 662
032 131 243 351 503 664
043 132 244 364 506 703
047 134 245 365 516 712
051 143 251 371 532 723
054 152 261 411 546 731
065 155 263 412 565 732
071 156 265 413 606 734
072 162 271 423 612 743
073 165 306 431 624 754
074 172 311 432 627
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