FX805 데이터 시트보기 (PDF) - CML Microsystems Plc

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FX805

Sub-audio signalling processor

CML Microsystems Plc 

Controlling Protocol ......

“Read CTCSS Rx Frequency Register” ......

The Integer (N) – Byte 1

A binary number representing ‘twice the number of

complete input sub-audio cycle periods’ counted during the

measurement period of 122.64ms

The Remainder (R) – Byte 0

A binary number representing the remainder part, R,

of 2 x Sub-Audio Input Frequency. ‘R = number of specified

measuring-clock cycles’ required to complete the specified

measurement period (See N). The clock-cycle frequency is

4166.6Hz

(REPLY DATA)

Byte 1

(MSB) – TRANSMITTED FIRST

15 14 13 12 11 10 9 8

“0” “0”

Integer (N)

76 5

“0” “0”

Byte 0

43

(REPLY DATA)

(LSB) – TRANSMITTED LAST

21 0

Remainder (R)

Fig. 6 Format of the CTCSS Rx Frequency Register

CTCSS Rx Frequency Register

Figure 6 (above) shows the format of the CTCSS Rx

Frequency Register.

Bits 8 (LSB) to 13 (MSB) are used to represent the Integer

(N). From Byte 1, valid values of N = 16 ≤ N ≤ 61.

ie. values of N less than 16 and greater than 61 are not

within the specified frequency band.

Bits 0 (LSB) to 5 (MSB) (Byte 0) are used to represent the

Remainder (R). From Byte 0, valid values of R = ≤ 31.

This register is not affected by the General Reset

command (01 ) and may adopt any random configuration at

H

Power-Up.

CTCSS Rx Frequency Measurement Formulæ

To assist in the production of ‘look-up’ tables and limit-values in the µController and provide guidance upon the determination

of N and R from a measured CTCSS frequency, the following formulæ show the derivation of the CTCSS Rx Frequency

(f

) from the measured data bytes (N and R).

CTCSS IN

fCTCSS IN

In the measurement period of 122.64ms there are N

cycles at 2 x f

and R clock-cycles at 4166.6Hz, for any

CTCSS IN

input frequency.

So

f

=

CTCSS IN

N xf

Hz

[1]

XTAL

1920 x (511 -R)

R = INT 511 – N x f

+ 0.5

[3]

XTAL

1920 x f

CT CSS IN

N = INT (1920 x 511 x f

)

[2]

CTCSS IN

f

XTAL

Calculate N first

Examples (fXTAL = 4.00MHz): fCTCSS IN = 100Hz N = 24 R = 11; fCTCSS IN = 250Hz N = 61 R = 3

NOTONE Timing

The input sub-audio signal is monitored by the Frequency

Assessment circuitry. Before any NOTONE action is enabled,

the FX805 must have achieved at least one successful “Tone

Measurement Complete” action.

If there is no signal or the signal is of a consistently poor

quality, the NOTONE Timer will start to charge via the timing

components. When the timing period has expired (at V /2),

DD

an Interrupt and a Status bit (NOTONE Timer Expired) are

generated. This is a one-shot function and is reset by a “Tone

Measurement Complete” interrupt.

9

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