CML Microcircuits CMX7031 Application Note page 22

Application Note
5.4 STATE 4: RX Startup
In order to reach this state, incoming RF carrier has caused the RSSI signal to exceed the
CMX7031's ADC1 high threshold. When this happens, STATUS Register ($C6) b8 = 1 and an IRQ is
issued.
Two types of incoming signals are expected in this application scenario; voice and FFSK / MSK data.
A voice call will be indicated by a CTCSS detection event, while incoming FFSK / MSK data will be
marked by the absence of the CTCSS detection.
Highlights of STATE 4 include:
•
Configure CMX7031 to receive signal from Disc input and pass signal through Input 1 to MSK
and CTCSS detectors.
•
Enable MSK and CTCSS detection.
•
Enable receive audio processing circuits.
The CMX7031 is configured for receive operation as follows:
Register
Register Name
Address
$B1 INPUT GAIN and OUTPUT
SIGNAL ROUTING
$C0 POWER DOWN CONTROL
$C2 AUDIO CONTROL
$C7 MODEM CONTROL
$CE INTERRUPT MASK
$C1 MODE CONTROL
The CMX7031 will issue an interrupt once the incoming signal has been identified, and the STATUS
register ($C6) can be read to determine the source of the interrupt. Expected interrupts include:
•
$C6 b4 = 1: 2400 bps FFSK / MSK data has been received. Proceed to STATE 7, FFSK /
MSK Rx.
•
$C6 b11 = 1: a CTCSS tone has been received. Proceed to STATE 5, Ring Tone Tx
(followed by STATE 6, Voice Rx).
Other interrupt sources indicate an error condition and should result in the firmware reverting to
STATE 3 Sleep Mode.
© 2007 CML Microsystems PLC
Register
Contents
0x0010
0x3050
0x6CC9
0x00A0
0x8B72
0x0049
Table 10: STATE 4 Register Settings
22 of 28
CMX7031
: An Example Core Design for a Complete Family Radio
Effect
Input 1 and Input 2 = 0dB, Input 1 signal from Disc,
MOD1 and MOD2 and Audio and Input 2 at bias.
Enabled: Disc amp, Input 1, bias block, xtal circuit.
Programming Register contents protected.
Enabled: compandor, deemphasis, 25kHz filter, 300Hz
HPF. CTCSS tone # 1 (67.0Hz) selected for receive.
Data packetizing mode, FFSK / MSK Mode 5 selected.
Enabled IRQs: CTCSS, AUXADC1, AUXADC2, FFSK /
MSK 2400 bps, RF status change
Subaudio source = Input 1, CTCSS enabled, FFSK /
MSK source = Input 1, 2400 bps enabled, Rx mode.
AN/2WR/7031/FRS/3 July 2007