Family Radio CTCSS 'Type 2' Encoder and Decoder
CMX808A
CTCSS TX FREQUENCY Register (Hex address $83)
This is a 16-bit register. Byte (1) is sent first. When the CTCSS transmitter is enabled, the bits 0 to 12
control the frequency of the transmitted CTCSS tones according to the formula below.
fXTAL (Hz)
A =
16 xfTONE (Hz)
where A is the binary number programmed into the 13 bits.
When Bit 7 (in the first 8 bits) is set to "1" the tone output is set at V
or NOTONE without regard to the
BIAS
number "A" programmed. When Bit 7 is "0" the programmed tone is set on the output. Programming bits
0 to 12 to "0" sets the output to V
AUDIO CONTROL register $80).
. Powersave is achieved by disabling the Tx (Bit 7 in the SUB-
BIAS
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 7 tones in the sub-audio band that will be decoded by the receiver.
Each tone is identified by its address in Bits 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
3
Byte 2
Bit Bit Bit Bit
Bit
2
Bit
1
Bit
0
Bit
7
Bit
6
Bit
5
Bit
4
Bit
3
Bit
2
Bit
1
Bit
0
7
0
0
0
0
0
0
0
6
0
0
0
0
1
1
1
5
4
0
0
1
1
0
0
1
0
1
0
1
0
1
0
<----------------------- N ----------------------->
<----------------------- R ----------------------->
N is the binary representation of the
following decimal number (n):
R is the nearest 6-bit binary
representation of (r), where:
n = INT (948982 x fTONE / fXTAL
)
r = ((237245/fXTAL) - (n/(4 x fTONE))) x 8400
Example: To program 100Hz when using the recommended 4.0MHz Xtal.
n = INT (948982 x 100 / 4.0 x 10^6)
=
INT (23.72) = 23
N = 010111 (binary)
r
=
=
=
((237245 / 4.0 x 10^6) - (23 / (4 x 100))) x 8400
15.21 (round up if exactly halfway)
15
R = 001111 (binary)
Thus the 12-bit code is 010111001111.
The Hex address represented by Bits 6, 5 and 4 in byte (1) is used as the code to indicate which tone has
been decoded. This code appears in Bits 2, 1 and 0 of the SUB-AUDIO STATUS register $81. The 7
programmed tones use Hex addresses $0 - $6. Address $7 should not be used.
2003 CML Microsystems Plc
10
D/808A/6
CMLMICRO [ CML MICROCIRCUITS ]
