FX828 Datasheet, PDF (20/34 Pages) CML Microcircuits – CTCSS/DCS/SELCALL Processor

CTCSS/DCS/SELCALL Processor
FX828
1.6 Application Notes
1.6.1 General
The FX828 is intended for use in radio systems where signalling is required for functions such as
trunking, control, selective calling or group calling.
The CTCSS fast/predictive detector is useful for the detection of occupied channels indicating either the
presence of any sub-audio tone, or range of tones, depending if it is set in fast detect or predictive mode.
This will increase the efficiency of scanning and trunking systems, reducing the average time allocated to
assessing each channel.
The facility to decode any of up to 15 programmed tones allows the use of tones for various signalling
functions such as masking a free channel or identifying sub groups within a user's groups.
Adjustable decoder bandwidths permit certainty and signal to noise performance to be traded when
congestion or range limits the system performance.
1.6.2 Transmitters
The CTCSS transmitter is enabled with Bit 7 in the SIGNALLING CONTROL Register ($80) and bit 1 in
the SIGNALLING SET UP Register ($82).
The Tx frequency is set using Bit 0 to Bit 12 in the CTCSS TX/FAST RX FREQUENCY Register ($83)
using the formula below:
A = ^{fXTAL (Hz)}
16 x f_TONE (Hz)
where A is the binary number programmed into the 13 bits.
When Bit 7 (in the first 8 bits) is set to "1" the tone output is set at V_BIAS or NOTONE without regard to the
number "A" programmed. When Bit 7 is "0" the programmed tone is set on the output. Programming the
bits 0 to 12 to "0" puts the Tx into powersave and the output goes to V_BIAS. Powersave is also achieved
by disabling the SUBAUDIO Tx and the CTCSS FAST DETECT (Bits 7 and 5 in the SIGNALLING
CONTROL Register $80).
The SELCALL transmitter is enabled with Bit 2 in the SIGNALLING CONTROL Register ($80).
The Tx frequency is set using Bit 0 to Bit 12 in the SELCALL TX Register ($8D) using the formula below:
A = ^{fXTAL (Hz)}
4 x f_TONE (Hz)
where A is the binary number programmed into the 13 bits.
When Bit 7 (in the first 8 bits) is set to "1" the tone output is set at V_BIAS or NOTONE without regard to the
number "A" programmed. When Bit 7 is "0" the programmed tone is set on the output. Programming the
bits 0 to 12 to "0" puts the Selcall Tx into powersave and the output goes to V_BIAS. Powersave is also
achieved by disabling the SELCALL TX ENABLE (Bit 2 in the SIGNALLING CONTROL Register $80).
The DCS transmitter is enabled by setting Bit 7 to "1" in the SIGNALLING CONTROL Register ($80)
having already set Bit 1 to "1" in the SIGNALLING SET UP Register ($82). Note that Bit 0 of this
SIGNALLING SET UP Register is used to select either 23-bit or 24-bit mode.
© 2009 CML Microsystems Plc
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