FX828 Datasheet, PDF (7/34 Pages) CML Microcircuits – CTCSS/DCS/SELCALL Processor

CTCSS/DCS/SELCALL Processor
FX828
1.5 General Description
The FX828 is a signalling encoder/decoder for use in land mobile radio equipment, see Figure 1.
The transmitter section of this device has independently controllable tone generators for sub-
audio (CTCSS) and inband (Selcall) signalling. It also features a DCS code generator, which may
be used in place of the CTCSS tone generator.
The receiver section of the FX828 has a fast/predictive CTCSS tone detector which operates in
parallel with a DCS decoder and a CTCSS/Selcall tone decoder. The latter is switchable to
perform either CTCSS or Selcall tone decoding of a user-programmable set of up to 15 tones. In
the CTCSS mode it performs a more accurate (but slower) analysis of the tones detected by the
fast/predictive CTCSS tone detector, which is a single detector that is switchable to provide either
a fast response to any CTCSS tone (FAST DETECT mode) or a fast response to a single user-
programmed CTCSS tone (PREDICTIVE mode).
Other functions on the FX828 are a comparator with programmable threshold level, a general
purpose timer and a summing amplifier with two adjustable gain blocks, which may be used for
two point modulation, for example. All FX828 functions are controlled by an external µC over the
C-BUS interface, a serial interface designed to reduce interference levels in radio equipment.
1.5.1 Software Description
Address/Commands
Instructions and data are transferred, via "C-BUS", in accordance with the timing information
given in Figure 4.
Instruction and data transactions to and from the FX828 consist of an Address/Command (A/C)
byte followed by either:
(i)
a further instruction or data (1 or 2 bytes) or
(ii) a status or Rx data reply (1 byte)
© 2009 CML Microsystems Plc
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