•• Fast CTCSS Detection•• Programmable Tone Decoder
•• Non Predictive Tone Detection•• Programmable Modulator Drivers
•• Low Power 3.3V/5V Operation•• Programmable Tone Encoders
•• Variable Gain Audio Filter•• Compact (SSOP and SOIC)
Packaging
1.1Brief Description
The FX818 is an innovative CTCSS Codec designed for the latest generation of Land Mobile Radio equipment.
The FX818 is full duplex and has many advanced features which assist the operation of modern CTCSS based
systems. The FX818 is electrically, physically and software compatible with the FX828. It permits
manufacturers to add new features to their equipment with minimal design changes.
The FX818 incorporates a programmable tone decoder which can be set to respond to between 1 and 15
CTCSS tones with minimum software intervention. In addition, a 'Fast' CTCSS detector can respond to a
single programmed tone in 60ms, or can be used to provide an output if any CTCSS tone is present at the
detector input. A high resolution tone encoder performs accurate generation of any CTCSS tone in current use.
High pass and low pass filters are included to provide filtering for CTCSS and Voice band signals. On chip
audio summation amplifier and digital adjustable modulator drivers ensure easy integration into equipment.
The FX818 along with the FX828 is offered in a choice of small SSOP and SOIC 24-pin packages. It may be
used with 3.0 to 5.5 volt supply.
1997 Consumer Microcircuits Limited
CTCSS Signalling ProcessorFX818
CONTENTS
SectionPage
1.0 Features ..........................................................................................................1
Note:As this product is still in development, it is likely that a number of changes and additions will be made to
this specification. Items marked TBD or left blank will be included in later issues.
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CTCSS Signalling ProcessorFX818
1.2Block Diagram
Figure 1 Block Diagram
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CTCSS Signalling ProcessorFX818
1.3Signal List
Package
D2/D5
SignalDescription
Pin No.NameType
1XTALNO/PThe inverted output of the on-chip oscillator.
2XTAL/CLOCKI/PThe input to the on-chip oscillator, for external
Xtal circuit or clock.
3SERIAL CLOCKI/PThe "C-BUS" serial clock input. This clock,
produced by the µController, is used for transfer
timing of commands and data to and from the
device. See "C-BUS" Timing Diagram (Figure
4).
4COMMAND DATAI/PThe "C-BUS" serial data input from the
µController. Data is loaded into this device in
8-bit bytes, MSB (B7) first, and LSB (B0) last,
synchronised to the SERIAL CLOCK. See
"C-BUS" Timing Diagram (Figure 4).
5REPLY DATAO/PThe "C-BUS" serial data output to the
µController. The transmission of REPLY DATA
bytes is synchronised to the SERIAL CLOCK
under the control of the CSN input. This 3-state
output is held at high impedance when not
sending data to the µController. See "C-BUS"
Timing Diagram (Figure 4).
6CSNI/PThe "C-BUS" data loading control function: this
input is provided by the µController. Data
transfer sequences are initiated, completed or
aborted by the CSN signal. See "C-BUS" Timing
Diagram (Figure 4).
7IRQNO/PThis output indicates an interrupt condition to the
µController by going to a logic "0". This is a
"wire-ORable" output, enabling the connection of
up to 8 peripherals to 1 interrupt port on the
µController. This pin has a low impedance
pulldown to logic "0" when active and a highimpedance when inactive. An external pullup
resistor is required.
The conditions that cause interrupts are
indicated in the IRQ FLAG register and are
effective if not masked out by a corresponding
bit in the IRQ MASK register.
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CTCSS Signalling ProcessorFX818
1.3Signal List (continued)
Package
D2/D5
SignalDescription
Pin No.NameType
8NC) No internal connection. Do not make
9NC) any connection to these pins.
10A/D CAPO/PAn internal reference voltage for the A to D,
decoupled to V
by an external capacitor.
SS
11NCNo internal connection. Do not make any
connection to this pin.
12V
13V
ss
BIAS
PowerThe negative supply rail (ground).
O/PA bias line for the internal circuitry, held at ½
. This pin must be decoupled by a capacitor
V
DD
mounted close to the device pins.
14RX AMP INI/PThe inverting input to the Rx input amplifier.
15RX AMP OUTO/PThe output of the Rx input amplifier and the input
to the audio filter section.
16RX AUDIO OUTO/POutput of the Rx audio filter section.
17NCNo internal connection. Do not make any
connection to this pin.
18SUM INI/P Input to the audio summing amplifier.
19SUM OUTO/P Output of the audio summing amplifier.
20MOD1 INI/P Input to MOD1 audio gain control.
21TX SUB AUDIO OUTO/POutput of the CTCSS tone generator.
22MOD1O/POutput of MOD1 audio gain control.
23MOD2O/POutput of MOD2 audio gain control.
24V
DD
PowerThe positive supply rail. Levels and voltages are
Notes:1. R2, R6 and C3 form the gain components for the Summing Amplifier. R6 should be chosen as
required from the system specification, using the following formula:
R2
Tx Sub Audio Gain=
−
R6
2. R3, R4, C5 and C7 form the gain components for the Rx Input Amplifier. R4 should be chosen
as required by the signal level, using the following formula:
R3
Gain=
−
R4
C7 x R4 should be chosen so as not to compromise the low frequency performance of this
product.
Figure 2 Recommended External Components
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CTCSS Signalling ProcessorFX818
1.5General Description
The FX818 is a programmable CTCSS sub-audio encoder/decoder for use in land mobile radio equipment, see
Figure 1.
The receiver section of the FX818 has a fast/predictive tone detector which operates in parallel with a tone
decoder. The latter decodes a user-programmable set of up to 15 tones and performs a more accurate (but
slower) analysis of the tones detected by the fast/predictive 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).
The high pass audio filter is designed to filter out the CTCSS sub-audio tones. The summing and modulation
amplifiers allow the audio modulation to be controlled digitally via the C-BUS. A general purpose timer is
included.
Each function, and the routing of signals, is flexible and may be configured or controlled by the user's software.
1.5.1Software 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 FX818 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)