Service Manual Part 1
8-
8 )
The primary task of the control section in the T2000 is to control the state of the radio at
all times, based both on user input, and activity of the internal circuitry. To achieve this,
the control section monitors the radio’s operation and responds to any changes with
various control signals.
The input shift registers are read by the microprocessor approximately 100 times per
second. The output shift registers are updated only when a control signal is required to
change, and the miscellaneous I/O is continually scanned.
In the majority of cases, a control output will change only in response to an input stimu-
lus, e.g. a control head key being pressed, receiver busy, etc. Some outputs may be
affected by more than one input or a sequence of events; this is particularly so in the
case of the mute gate control line. Its operation may be affected by a number of external
conditions and even some generated in the microprocessor.
For operation of the T2000 Series II control heads, refer to Figures 2.8 to 2.10.
88 1141+=)1+,#)6
Transmitter speech from the microphone is preamplified and fed into an automatic level
control circuit which also has two mute facilities (one for options and one for the micro-
processor). The speech is pre-emphasised and high pass filtered to reduce CTCSS com-
ponents, then passes via the RF PCB to the limiter on the TCXO/Tx audio PCB.
DCS/CTCSS signals are generated by the microprocessor and are filtered by a low pass
filter before being passed to the level potentiometer on the TCXO/Tx audio PCB. A five
tone Selcall module is available which is directly interfaced to the microprocessor.
Selcall tones are fed to the limiter on the TCXO/Tx audio PCB.
Receiver audio from the IF PCB passes through a low pass filter where it is split into sig-
nalling and speech paths. Five tone signals are coupled to the five tone module. DCS/
CTCSS passes through a low pass filter and limiter before arriving at the microproces-
sor. Speech is de-emphasised and passed through one or two high pass filters, depend-
ing on the signalling used. Processed speech passes through the mute to an amplifier
where speech and progress tones are summed. The signal then passes via the volume
control to the audio power amplifier on the RF PCB.