CTCSS/DCS/SELCALL Processor

FX828

© 2009 CML Microsystems Plc

20

D/828/4

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

f

(Hz)

16 x f

(Hz)

XTAL

TONE

=

where A is the binary number programmed into the 13 bits.

number "A" programmed. When Bit 7 is "0" the programmed tone is set on the output. Programming the

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

f

(Hz)

4 x f

(Hz)

XTAL

TONE

=

where A is the binary number programmed into the 13 bits.

number "A" programmed. When Bit 7 is "0" the programmed tone is set on the output. Programming the

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.