CTCSS Signalling Processor
FX818
1.5
General 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.
1.5.1
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 FX818 consist of an Address/Command (A/C) byte
followed by either:
(i)
(ii)
8-bit Write Only Registers
HEX
ADDRESS/
COMMAND
REGISTER
NAME
BIT 7
(D7)
BIT 6
(D6)
BIT 5
(D5)
BIT 4
(D4)
BIT 3
(D3)
BIT 2
(D2)
BIT 1
(D1)
BIT 0
(D0)
a further instruction or data (1 or 2 bytes) or
a status or Rx data reply (1 byte)
$01
GENERAL
RESET
N/A
N/A
N/A
N/A
N/A
N/A
N/A
N/A
CTCSS
$80
SUB-AUDIO
CONTROL
TX
ENABLE
DECODER
ENABLE
FAST
DETECT
ENABLE
0
0
FAST CTCSS
MODE
DETECT/
PREDICTIVE
0
0
0
CTCSS DECODER BANDWIDTH
$82
SUB-AUDIO
SET-UP
MSB
BIT 3
BIT 2
BIT 1
BPF
$88
GENERAL
CONTROL
GENERAL
$8B
PURPOSE
TIMER
MSB
BIT 7
BIT 6
GPT
$8E
IRQ
MASK
0
IRQ
MASK
0
0
BIT 5
BIT 4
BPF
ENABLE
BPF
UN-MUTE
6dB
PAD
0
LSB
BIT 0
0
0
0
TIMER
0
0
ENABLE
TIMER
RE-CYCLE
GENERAL PURPOSE TIMER
LSB
BIT 3
CTCSS
IRQ
MASK
BIT 2
CTCSS
FAST IRQ
MASK
0
0
BIT 1
BIT 0
©
1997
Consumer Microcircuits Limited
7
D/818/4
CMLMICRO [ CML MICROCIRCUITS ]
