Controlling Protocol ......
“Write to CTCSS Tx Frequency/NRZ Baud Rate Register”
Command Data.
The information loaded to this register will set either the:
(a) CTCSS Tx Tone Frequency
(b) NRZ Tx Baud Rate
(c) NRZ Rx Baud Rate
f
CTCSS OUT
R
NRZ Tx
R
NRZ Rx
– A/C 73
H
(7B
H
), followed by 2 bytes of
The chosen mode for this register (a, b or c) is determined by the FX805 operational mode enabled by the Control Register
(Table 3), as shown in the table below.
Control Register Bits
7
6
5
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
FX805 Mode
Enabled
CTCSS Decode
NRZ Decode
CTCSS Encode
NRZ Encode
CTCSS Encode and Decode
NRZ Encode and CTCSS Decode
NRZ and CTCSS Decode
NRZ Decode
CTCSS Tx/NRZ Baud Rate
Register Function
NRZ Rx Baud Rate
CTCSS Tx Frequency
NRZ Tx Baud Rate
CTCSS Tx Frequency
NRZ Tx Baud Rate
NRZ Rx Baud Rate
NRZ Rx Baud Rate
Table 5 CTCSS Frequency/NRZ Baud Rate Register Configurations
Data Format
Data is transmitted, via “C-BUS,” to this register as 2 bytes of Command Data (1 and 2) distributed as command words P and
Q, in the form illustrated in Figure 7. This register is not affected by the General Reset command (01
H
) and may adopt any
random configuration at Power-Up.
(COMMAND DATA)
(MSB) – LOADED FIRST
Byte 1
12
11
“0”
10
9
8
7
6
5
Q
Byte 0
4
3
2
(COMMAND DATA)
(LSB) – LOADED LAST
15
14
P
13
1
0
Fig.7 Format of the CTCSS Tx Frequency/NRZ Baud Rate Register
Command Words P and Q
With reference to Figure 7, the two data words, P and Q, loaded to this register are interpreted as:
P
= a binary number to set the Tx Sub-Audio Lowpass Filter bandwidth (applicable to NRZ Encode and CTCSS
Encode modes).
Q
= a binary number to set the frequency or baud rate of the selected function (see Table 5).
Command Word ‘P’
Bits
15 14
0
0
0
0
0
0
1
0
0
1
1
1
1
0
LSB
13 12
1
1
0
0
1
1
0
0
1
0
1
0
1
0
Bits 12 to 15 are used to produce the data word ‘P’ as
shown in Table 6 (left). The cut-off frequency f
CO
(0.5dB
point) of the Tx Sub-Audio Lowpass Filter is calculated as:
f
CO
=
f
XTAL
32 x 208.33 x
‘P’
so
‘P’
=
f
XTAL
32 x 208.33 x f
CO
Table 6 is given as an example and calculated using a Xtal/
clock (f
XTAL
) frequency of 4.00MHz. As illustrated, only values
of ‘P’ of
2 to 8
are usable.
‘P’
2
3
4
5
6
7
8
LPF Bandwidth
300Hz
200Hz
150Hz
120Hz
100Hz
85.7Hz
75Hz
Table 6 Valid Values of ‘P’
10
CMLMICRO [ CML MICROCIRCUITS ]
