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CMX808A

Family Radio CTCSS ‘Type 2’ Encoder and Decoder

CML Microcircuits 

Family Radio CTCSS 'Type 2' Encoder and Decoder

TONE CLONING Register (Hex address $9C)

This register enables and disables tone cloning as shown below:

$9C = $01 enables tone cloning.

$9C = $00 disables tone cloning.

Figure 4 shows the tone cloning routine.

CMX808A

8-bit Read Only Registers

HEX

ADDRESS/

COMMAND

REGISTER

NAME

BIT 7

(D7)

$81

SUB-AUDIO

0

STATUS

BIT 6

(D6)

0

BIT 5

(D5)

0

BIT 4

(D4)

BIT 3

(D3)

BIT 2

(D2)

BIT 1

(D1)

BIT 0

(D0)

CTCSS RX TONE

0

TONE

MSB

LSB

DECODE BIT 2

BIT 1

BIT 0

Read Only Register Description

SUB-AUDIO STATUS Register (Hex address $81)

Reading the SUB-AUDIO STATUS register clears the interrupt (IRQN).

This register is used to indicate the status of the device as described below:

(Bits 7, 6, 5 and 4)

Reserved for future use. These will be set to "0" but should be ignored by user's

software.

TONE DECODE

(Bit 3)

This bit indicates the status of the tone decoder. A "1" indicates a tone has

been detected (TONE DECODE) and a "0" indicates the loss of the tone

(NOTONE).

TONE DECODE means that a tone has been decoded and its characteristics

are defined by the bandwidth (see SUB-AUDIO CONTROL register $80, Bits 5,

4, 3 and 2) and the CTCSS RX TONE number (see SUB-AUDIO STATUS

register $81, Bits 2, 1 and 0).

When Bit 6 in the SUB-AUDIO CONTROL register $80 is set to "0" the TONE

DECODE Bit 3 will be set to "0".

Identification of a valid tone which is not in the pre-programmed list of up to 7

tones will cause the decoder to move to the TONE DECODE state with the RX

TONE address of "111" in Bits 2, 1 and 0; indicating a valid but unrecognised

tone. Loss of tone will cause the NOTONE timer to be started. If loss of tone

continues for the duration of the time-out period, then the decoder will move to

NOTONE state and the identification of pre-programmed tones will start again.

The time-out period is not user adjustable.

CTCSS RX TONE

(Bits 2, 1 and 0)

These three bits hold a Hex number. Numbers $0 to $6 represent the address

of the CTCSS tone decoded according to the tones programmed in the CTCSS

RX PROGRAM register $84. The Hex number $7 indicates the presence of

any tone that is not described by CTCSS DECODER BANDWIDTH (Bits 5, 4, 3

and 2 in the SUB-AUDIO CONTROL register $80) and CTCSS FREQUENCY

(Bits 11 to 0 in the CTCSS RX PROGRAM register $84).

© 1999 Consumer Microcircuits Limited

11

D/808A/5

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