FX828 Datasheet, PDF (14/34 Pages) CML Microcircuits – CTCSS/DCS/SELCALL Processor

CTCSS/DCS/SELCALL Processor
FX828
When Bit 7 in byte (1) is set to "1" the tone output is set at V_BIAS or NOTONE without regard to the
number "A" programmed. When Bit 7 is "0" the programmed tone is set on the output. Programming the
bits 0 to 12 to "0" puts the Tx into powersave and the output goes to V_BIAS. Powersave is also achieved
by disabling the SUBAUDIO Tx and the CTCSS FAST DETECT.
RX TONE PROGRAM Register (Hex address $84)
This is a 16-bit register. Byte (1) is sent first. The two bytes are used to program the centre frequencies of
up to 15 tones in either the audio or sub-audio band that will be decoded by the receiver.
Each tone is identified by its address in bits 7, 6, 5 and 4 of byte (1). The remaining 12 bits contain the
data representing the tone frequency according to the formula below. If a tone is not required the 12 bits
should be set to zero.
Byte 1
Byte 2
Bit Bit Bit Bit Bit
Bit
Bit
Bit
Bit
Bit
Bit
Bit
Bit
Bit
Bit
Bit
7 65 4
3
2
1
0
7
6
5
4
3
2
1
0
0 0 0 0 <------------------------ N -----------------------> <----------------------- R ------------------------>
0001
0 0 1 0 N is the binary representation of the
R is the nearest 6-bit binary
0 0 1 1 following decimal number (n):
representation of (r), where:
0100
0101
0110
0 1 1 1 SUBAUDIO (CTCSS)
SUBAUDIO (CTCSS)
1 0 0 0 n = INT (948982 x f_TONE / f_XTAL)
1001
r = ((237245/f_XTAL) - (n/(4 x f_TONE))) x 8400
1010
1011
1 1 0 0 INBAND (SELCALL)
INBAND (SELCALL)
1 1 0 1 n = INT (83036 x f_TONE / f_XTAL)
1110
r = ((20759/f_XTAL) - (n/(4 x f_TONE))) x 96000
Example: To program 100Hz when using the recommended 4.032MHz Xtal in SUBAUDIO
(CTCSS) mode.
n = INT (948982 x 100 / 4.032 x 10^6)
= INT (23.536) = 23
N = 010111 (binary)
r = ((237245 / 4.032 x 10^6) - (23 / (4 x 100))) x 8400
= 11.26 (round up if exactly halfway)
R = 11
= 001011 (binary)
Thus the 12-bit code is 010111001011
The Hex address represented by bits 7, 6, 5 and 4 in byte (1) is used as the code to indicate which tone
has been decoded. This code appears in bits 3, 2, 1 and 0 of the SELCALL and SUB-AUDIO STATUS
Register (Hex address $81). The 15 programmed tones use Hex addresses $0 - $E.
© 2009 CML Microsystems Plc
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