FX818D5 View Datasheet(PDF) - CML Microsystems Plc
Part Name
Description
MFG CO.
'FX818D5' PDF : 26 Pages View PDF
CTCSS Signalling Processor
FX818
When Bit 7 (in the first 8 bits) is set to "1" the tone output is set at VBIAS 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 VBIAS. Powersave is also achieved by disabling
the Tx and the FAST DETECT.
CTCSS RX 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 the 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
Bit Bit Bit Bit Bit
Bit
Bit
Bit
Bit
Bit
7 65 4
3
2
1
0
7
6
0 0 0 0 <-------------------- N -------------------- >
0001
0010
0011
0100
0 1 0 1 N is the binary representation of the
0 1 1 0 following decimal number (n):
0111
1 0 0 0 n = INT (948982 x fTONE / fXTAL)
1001
1010
1011
1100
1101
1110
Byte 2
Bit
Bit
Bit
Bit
Bit
Bit
5
4
3
2
1
0
<-------------------- R ------------------->
R is the nearest 6-bit binary
representation of (r), where:
r = ((237245/fXTAL) - (n/(4 x fTONE))) x 8400
Example: To program 100Hz when using the recommended 4.032MHz Xtal.
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 SUB-AUDIO STATUS Register (Hex address
$81). The 15 programmed tones use Hex addresses $0 - $E.
© 1997 Consumer Microcircuits Limited
12
D/818/4
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