CTCSS Signalling Processor

FX818

© 1997 Consumer Microcircuits Limited

14

D/818/4

8-bit Read 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)

CTCSS

CTCSS RX TONE

$81

SUB-AUDIO

0

FAST

0

TONE

MSB

LSB

STATUS

TONE

DECODE

BIT 3

BIT 2

BIT 1

BIT 0

GP TIMER

CTCSS

CTCSS FAST

$8F

IRQ FLAG

0

IRQ

0

0

IRQ

IRQ

0

0

FLAG

FLAG

FLAG

Read Only Register Description

SUB-AUDIO STATUS Register (Hex address $81)

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

(Bit 7)

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

software.

CTCSS FAST TONE

(Bit 6)

When Bit 5 in the SUB-AUDIO CONTROL Register and Bit 3 in the SUB-AUDIO

SET-UP Register are set to enable FAST CTCSS DETECT mode, this bit will be

set to "1" if a periodic tone is detected. If no periodic tone is detected this bit will

be "0".

When bits 5 and 3 are set to enable FAST CTCSS PREDICTIVE mode, this bit

will be set to "1" if a periodic tone that matches the frequency programmed in the

CTCSS TX/FAST RX Register is detected. If no match is found this bit will be

"0".

When Bit 5 in the SUB-AUDIO CONTROL Register is set to "0" this bit will be

"0".

(Bit 5)

Reserved for future use. This will be set to "0" but should be ignored by the

user's software.

TONE DECODE

(Bits 4)

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 SET-UP Register bits 7, 6, 5 and 4)

and the CTCSS RX TONE number (See SUB-AUDIO STATUS Register bits 3,

2, 1 and 0).

When Bit 6 in the SUB-AUDIO CONTROL Register is set to "0" the TONE

DECODE bit 4 will be set to "0".

Identification of a valid tone which is not in the pre-programmed list of up to 15

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

TONE address of "1111" in bits 3, 2, 1 and 0; indicting 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 timeout period, then the decoder will move to

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