TM 11-5820-890-30-4
12-3. ICOM I/O SECTION. Continued
TF from analog data devices is converted to 16 kb/s digital data by the ICOM control module prior to transmis-
sion. TF data is hard limited by the ICOM data I/O module. This process converts the 1.2 kHz and 2.4 kHz FSK
signal from the data device into a 1.2 kHz and 2.4 kHz digital signal. This signal is input to the ICOM control
module where it is demodulated. 1.2 kHz is output as a logic 1 and 2.4 kHz is output as a logic 0. This signal is
then interleaved up to 16 kb/s and transmitted identically to low speed digital data. In receive, the TF signal is
converted back into a 1.2 kHz and 2.4 kHz digital signal and output to the ICOM data I/O module where it is low
pass filtered into a sine wave.
When the 16K data rate is selected the data is handled transparently. No code words are used, and no interleav-
ing or deinterleaving takes place. The data passes through the ICOM control module without being operated
upon.
The ICOM control module generates control signals used in the ICOM I/O section to control and route all digital,
TF, and voice signals. All receive voice signals (PT and CT) are routed through the ICOM control module. Trans-
mit PT voice is also routed through this module. Transmit CT voice is routed directly to the COMSEC module from
the ICOM data I/O module for encryption. PT sidetone is generated by this module by attenuating the transmit
signal and routing it along the receive audio path. Transmit CT sidetone is provided by the COMSEC module and
is routed through the ICOM control module along the same path as receive CT voice. All of the receive CT,
receive PT, and sidetone signals are routed to a single output called receive analog/sidetone (RCV ANLG/ST),
which goes to the ICOM data I/O module.
The ICOM data I/O module is the interface between the front panel AUD/DATA and AUD/FILL connectors and the
ICOM I/O section of the RCU. Voice, digital data, and TF data are multiplexed onto the AUD/DATA connector.
Voice and COMSEC fill lines are multiplexed onto the AUD/FILL connector. Fill information and command and
control data (CCD) to and from an external fill device are switched to the fill routing module when a fill device is
attached. When no fill device is attached, AUD/FILL lines are switched to a handset interface.
Detection of analog and digital devices attached to the AUD/DATA connector is provided to the ICOM control
module by the ICOM data l/O module. It converts +/-5 V p digital data from external devices to logic 0 and logic 1
levels for transmit processing by the ICOM control module. The ICOM data I/O module sums voice signals from
the AUD/DATA and AUD/FILL connectors, filters and amplifies the audio, and contains an AGC circuit which
maintains a constant output voltage. The gain of the amplifier stage is increased when the front panel VOL switch
is pulled out (WHSP mode). The transmit audio line is output to the ICOM control module.
Receive analog/sidetone and the FH alarm from the main switching module are summed in the ICOM data l/O
module, filtered, and amplified. The front panel VOL switch sets the final output level of the received audio.
Receive TF data is input to the ICOM data I/O module by the ICOM control module at logic 0 and logic 1 levels. The
ICOM data l/O module filters TF data back into a sine wave for output at the AUD/DATA connector. The output
level of TF data is fixed and is unaffected by the VOL switch. Received digital data and the digital data clock (used
in both transmit and receive) are input to the ICOM data I/O module from the ICOM control module. These signals
are input at logic 0 and logic 1 levels. The ICOM data I/O module converts them to +/- 5 V p signals prior to output
at the AUD/DATA connector.
The fill routing module is the interface to the fill portion of the AUD/FILL connector. It selects the fill path in the
ICOM data I/O module when it detects that an external fill device has been attached. Fill device logic levels are
0 V dc and -6.75 V dc. The fill routing module converts these to logic 0 and logic 1 levels prior to fill processing.
Outputs to the fill device are converted from logic 0 and logic 1 levels to 0 V dc and -6.75 V dc levels by this
module. COMSEC variables are loaded into the RCU using the following process:
1. The fill routing module detects the presence of the attached fill device and informs
the control module via an asynchronous link.
2. The control module issues a fill request to the fill routing module via the link when
the LOAD/0 key is pressed.
12-8
