80
Programmable I/O Lines
TM8000 3DK Hardware Developer’s Kit
Application Manual
September 2003
© Tait Electronics Ltd
3.3
Audio Tap In and Tap Out Lines
This section describes the general design principles for use of the
programmable audio tap in and tap out lines.
Audio Tap Point
Philosophy
The radio provides the ability to input and output audio at various tap points
in the transmit and receive audio paths. This removes the need of tapping
wires into the circuitry of the radio. The tap points and the type of tap are
programmed into the radio and cannot be modified by the radio user.
Available Audio
Tap In and Tap Out
Lines
The following lines are available to tap into and tap out of the audio paths:
For details on the connector pin-outs and electrical characteristics of these
lines refer to
“Description of the Radio Interfaces” on page 15
Input/Output
Circuitry
shows a simplified circuit diagram of the audio tap in and tap
out lines. Protection circuits are not shown.
The signal source for the audio tap out line comes from the DSP audio path
(refer to
for details) and is fed to a digital to analogue converter
at 48000 samples per second. The converter output is low pass filtered at
12kHz to remove alias components and fed to a buffer amplifier. The buffer
amplifier output is DC coupled to the AUD_TAP_OUT line and has a DC
offset of nominally 2.3V. The DC offset is affected by Rx carrier frequency
error for taps R1, R2 and R4. Full scale output level is nominally 4 V
p-p
with no load (for more information refer to
Table 3.7
Audio tap in and tap out lines
Signals
Connector
Direction
AUD_TAP_IN
auxiliary connector
internal options connector
input only
AUD_TAP_OUT
auxiliary connector
internal options connector
output only
Figure 3.12
Audio tap input and output - simplified circuit diagram
digital-to-
analogue
converter
12kHz
LPF
buffer
600
AUD_TAP_OUT
DSP
audio
path
analogue-
to-digital
converter
22kHz
LPF
AUD_TAP_IN
DSP
audio
path
3.3V
220k
180k
4.3V
2.3V
0.3V
Full-scale output level
(no load)
2.5V
1.5V
0.5V
Full-scale input level
3.7Hz
HPF