CTCSS Signalling Processor

FX818

© 1997 Consumer Microcircuits Limited

7

D/818/4

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)

a further instruction or data (1 or 2 bytes) or

(ii)

a status or Rx data reply (1 byte)

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)

$01

GENERAL

N/A

N/A

N/A

N/A

N/A

N/A

N/A

N/A

RESET

CTCSS

$80

SUB-AUDIO

TX

DECODER

FAST

DETECT

CONTROL

ENABLE

ENABLE

ENABLE

0

0

0

0

0

CTCSS DECODER BANDWIDTH

FAST CTCSS

$82

SUB-AUDIO

MSB

LSB

MODE

SET-UP

BIT 3

BIT 2

BIT 1

BIT 0

DETECT/

PREDICTIVE

0

0

0

BPF

$88

GENERAL

BPF

BPF

6dB

TIMER

TIMER

CONTROL

ENABLE

UN-MUTE

PAD

0

0

0

ENABLE

RE-CYCLE

GENERAL

GENERAL PURPOSE TIMER

$8B

PURPOSE

MSB

LSB

TIMER

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

GPT

CTCSS

CTCSS

$8E

IRQ

IRQ

IRQ

FAST IRQ

MASK

0

MASK

0

0

MASK

MASK

0

0