12-3. ICOM I/O SECTION. Continued
3. The fill routing module issues a fill request to the fill device and receives a variable.
4. The fill routing module performs a parity check on the variable.
5. If the variable does not have good parity, the fill routing module informs the control
module and BAD is displayed.
6. If the variable has good parity, the variable is loaded into the COMSEC module at the
location selected from the keypad.
Data rate information is sent to the fill routing module via the asynchronous link and is transferred to the ICOM
control module for selection. The COMSEC * ON/OFF function is selected by the fill routing module when in-
structed by the asynchronous link. The fill routing module monitors the length of time the COMSEC switch is left in
the Z position and activates the COMSEC Zero All-N (ZA-N) line when the switch is left there for 5 seconds or
The COMSEC module encrypts in transmit, and decrypts in receive, all forms of baseband when the COMSEC
switch is in the CT position. All transmissions leaving and received signals entering the COMSEC module are 16
kb/s digital. Voice and analog data signals from the ICOM data I/O module are converted to digital prior to
encryption by the COMSEC module. Sync signals are inserted during the pauses in voice transmissions, and
these sync signals are removed at the receive end. Digital data is input to the COMSEC module for encryption
after processing by the ICOM control module. At the receive end this is reversed.
The COMSEC module gets variables and variable select information from the fill routing module. Variables for
operation are selected by moving the CHAN switch or by pressing the CMSC and CHG keys on the keypad.
Variables selected by moving the CHAN switch are selected as follows:
(TEK stands for Transmission Encryption Key and KEK stands for Key Encryption Key.)
The COMSEC module uses a hold voltage to retain its variables when the RCU is in STBY, as described in the
ICOM power supply portion of this section. COMSEC variables are zeroed or erased when the COMSEC switch is
placed in the Z position or when either of the RCU covers is removed.
12-4. SPEAKER AMPLIFIER SECTION.
The speaker amplifier section consists of two modules. They are:
Circuit Card Assembly - Speaker Amplifier 19A6 (speaker amplifier module)
Electronic Component Assembly - DC power filter 19A12 (DC power filter module)
The module locations are shown in figure 12-5.