Sub-Audio Signaling Processor
Page 13 of 24
MX805A
5.2.3 Read Status Register –A/C 71 (79 ) followed by 1 byte of Rely Data.
H
H
The Status Register indicates the operational condition of the MX805A. Bits 0 to 5 are set individually to
indicate specific actions within the device. When a Status bit is set to a logic “1”, and Interrupt Request (IRQ)
output is generated. A read of the Status Register will reset the Interrupt and ascertain the state of this
register. Table 7 shows the conditions indicated by the Status bits.
Setting Set By
Logic Cleared By
Logic
MSB
Received First
Not Used
7, 6
5
0
1
Not Used
0
0
NRZ data transmission complete.
No new data is loaded.
1. Write to NRZ Data Reg., or
2. General Reset, or
3. NRZ Encoder Powersave
4
3
2
1
0
NRZ TX Data Buffer ready for next
data byte.
1
1
1
1
1
1. Write to NRZ TX Data Reg., or
0
0
0
0
0
2. General Rest, or
3. NRZ TX Powersave
New NRZ RX data received before
last byte was read.
1. Read NRZ RX Data Reg., or
2. General Reset, or
3. NRZ Decoder powersave
1 byte of NRZ data received
NoTone timer period expired
RX Tone Measurement Complete
1. Read NRZ RX Data Reg., or
2. General Reset, or
3. NRZ Decoder powersave
1. Read Status Register, or
2. General Rest, or
3. CTCSS Decoder Powersave
1. Read Status Register, or
2. General Reset, or
3. CTCSS Decoder Powersave
Table 7: Status Register
5.2.4 Read CTCSS RX Frequency Register –A/C 72 (7A ) followed by 2 bytes of Reply Data
H
H
5.2.4.1 Measurement of CTCSS RX Frequency (f
)
CTCSS IN
The input sub-audio signal (f
) is filtered, doubled and measured in the Frequency Counter over the
CTCSS IN
“measurement period” (122.64ms) (4.0MHz Xtal).
The measuring function counts the number of complete input cycles occurring within the measurement period
and the number of measuring-clock cycles necessary to make up one period.
When the measurement period of a successful decode is complete, the RX Tone Measurement bit in the
Status Register and the Interrupt bit are set.
The CTCSS RX Frequency Register will now indicated the sub-audio signal frequency (f
) in the form
CTCSS IN
of 2 data bytes (1 and 0) as illustrated in Figure 6.
Measurement Period
Measuring
Complete
Input
Cycle
Complete
Input
Cycle
Complete
Input
Cycle
Complete
Input
Cycle
Complete
Input
Cycle
Clock
Cycles
FILTERED AND DOUBLED SUB-AUDIO INPUT SIGNAL 2 x f
CTCSS IN
N
R
Figure 5: Measurement of a CTCSS RX Frequency
ã2001 MX-COM, Inc.
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Doc. # 20480116.006
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