Company Confidential
39
Raveon Technologies Corp.
11. Audio Pass-Through Mode
The
M8S
modem may be configured to pass the receive audio out its I/O
connection and when keyed, pass the audio on pin
The IO pins on the 20-pin I/O header related to the audio pass-through mode
are:
Pin #
Function
I/O
Function
1
GND
-
Ground
2
Vcc
I
DC Input
7
Enable
I
Low (<.7V) to shut down the module. High (>2.5V) to enable it.
11
RSSI
0
Receiver signal strength indicator
13
TX Audio In
I/O
General purpose digital I/O. 3V digital logic from CPU on M8. If the
Audio option is used, this pin is used to input transmit audio.
10
PTT
I/O
In audio pass-through mode, functions as PTT. 0=TX, 1=RX.
17
RX Audio Out
O
Receive and transmit audio output for factory test. Do not connect to
anything. If the AUDIO option is used, this pin is the receive audio
output.
19
GND
-
System Ground to M8
Pin 12 is the Push To Talk (PTT) input. It has a pull-up resistor of about 10K on
it. When PTT is low, the transmitter in the M8T will turn on, and output the audio
signal that is on pin 13.
When PTT is high, the M8T is in the receive mode, and the receive audio will be
output on pin 17.
There are a few commands designed specifically for use in configuring the
operation of the M8S in audio pass-through mode.
AFDC
Audio input DC ofset
– The DC bias level on the audio input in millivolt.
Adjust this setting so the audio transmissions are on the center of the
channel. Set to 0 to have the M8S auto-detect the average.
Range: 0-
3300
mV
1650
AFLVL
Audio input level gain
– internal gain of the audio input signal, in % .
Adjust this setting for the audio input deviation level.
Range: 0-
2000%
mV
100
AFLIM
Audio deviation limit
– Sets the peak audio deviation limit for TX audio
in the audio pass-through mode. In % of data deviation 100% limits audio
to same as data. .
Range: 0-
300%
100
TXTOT
Transmit Time-Out-Timer
– Sets the maximum number of seconds that
the M8S will stay transmitting when the PTT input is asserted.
Range: 0-500
seconds
10
The transmit audio input pin 13 is designed to have audio sent in with a 1.66 V
DC bias. If the audio input has a different DC bias voltage, the M8T can be
reconfigured to use the different DC bias offset. The
AFDC
sets the nominal DC
boas voltage. Note, the analog input range of the M8S is 0-3.3V. Ideally bias the
DC input to 1.66V or AC couple it with a capacitor and add two bias resistor to
ground and 3.3V. To have the M8S determine the DC bias input automatically
