2-14. PRIMARY CONTROL SIGNALS. Continued
The keyboard is made up of 16 switches (keys). They are arranged in a four-by-four switch matrix. The control
module checks the X and Y lines to see if a key has been pressed. The Y lines (rows) are normally at logic 1. The
X line (columns) are normally at logic 0. When a key is pressed, the Y line will be pulled to logic 0. The X line will
be pulled high (to about 6 V dc).
2-15. FREQUENCY HOPPING OPERATIONS.
The programming for FH operation is stored in the ECCM module ROM. The control module executes these
commands to control the RT while in FH.
Received FH signals are digital signals. The switching module digital processing produces bit synchronized data
(BS DATA). See figure 2-10. BS DATA is the RCV FH signal synchronized with the internal RT clocks and
converted to RT digital signal levels.
BS DATA goes to the ECCM module interleave circuits. The interleaver
removes synchronization and frequency hopping information that is embedded in the signal.
deinterleaving, the signal is reclocked at a 16 kb/s rate. It is now the FH DATA signal. In RCV DATA mode, FH
DATA is routed to the switching module. When receiving audio, FH DATA is converted back to an analog signal
by the continuously variable slope detector (CVSD) in the ECCM module. The RCV FH AUDIO output is also
routed to the switching module.
Two signals are required by the ECCM module during FH transmit. They are BS DATA and XMT PT AUDIO. BS
DATA goes directly to the interleave. It is interleaved with the synchronization and FH information needed by the
receiving RT to coordinate communications.
The CVSD converts PT AUDIO to a 16 kb/s digital signal output as
CVSD DATA to the interleave. It too is interleaved with data, reclocked to 20 kb/s, and output on the FH DATA
line to the switching module.
The interleave supplies the control and data signals needed by the time sync/correlator. The correlators
function is to synchronize the operation of the RT and the ECCM module.
It manipulates control signal outputs
such as HOP TIME and SYNC. These and others control RT operations in FH mode.
They shut down
reception/transmission during frequency shifts, provide the next frequency to the control module (via the data
and address busses), and supply clocking for the ECCM module.
The ECCM module is also responsible for: storage of the FH operation programming, generation of random
numbers for hopping frequency selection, and processing and storage of FILL data. The RT chooses the
frequencies in FH by pseudorandom number generation. The TRANSEC variable, TOD, and net ID number are
used to select the next frequency. The control module uses the hopset and lockout set to create a look-up table
in memory of frequencies for the net. The ECCM module picks one of these frequencies from the table. The
result is passed to the control module over the data bus. The control module informs the rest of the modules of
the frequency selected by the SERIAL DATA LINE.
The RT self-test is performed at several levels. When the FCTN switch is set to TST, the control module begins
the self-test routines.
The RT receive path, ECCM module, data rate adapter section of the ICOM control
module, the fill routing module and COMSEC module are checked.
A test line to the SYSTEM connector is
activated. This allows the RT to report the results of SNAP self-tests. A self-test of the remote control modules
can be performed separately.
a. Display Checks. The RT display is the first section tested in self-test. The first display is E C. E
shows that the ECCM module is present, and C shows that the COMSEC module is present. The ECCM
module grounds the FH HERE-N line to show its presence to the control module, and the COMSEC module
grounds the GND CLOS-B line to show its presence. See figure FO-8. If either module is absent, its letter in the
display is replaced by a dash (-).