TM 11-5820-890-30-4
12-3. ICOM I/O SECTION. Continued
The ICOM power supply provides power to the ICOM I/O section of the RCU. It derives dc output power from the
+10 V dc and -10 V dc outputs of the power supply. The +10 V dc input is shunt regulated to provide a RED +9.5 V
dc output for use by the ICOM I/O section. The RED +9.5 V dc output is series regulated to provide RED +5.5 V dc
for use by logic circuits in the ICOM I/O section. The -10 V dc input is shunt regulated to provide a RED -9.5 V dc
output, and this output is series regulated to provide a RED -6.75 V dc output. The shunt regulators are enabled
in active CT modes and when COMSEC variables are being loaded. The destination of these output voltages is
listed in table 12-1.
Table 12-1. ICOM Power Supply Output Destinations
Voltage (V dc)
Destinations (module-pin)
RED +9.5
19A8-71 , 19A94, 19A10-19, 19A11-52
RED +5.5
19A8-69, 19A9-m, 19A10-9
RED -9.5
19A8-72, 19A9-n, 19A10-10
RED -6.75
19A8-70, 19A9-o
The ICOM power supply has a digital buffer that buffers and isolates digital and control signals crossing the
red/black boundary.
The ICOM power supply provides a hold voltage for the control module that is used as its primary power source
for the Random Access Memory (RAM) circuits. The hold voltage is regulated from the primary battery input. A
hold voltage is also provided to the COMSEC module and is used to retain its variables. Input to this circuit is
provided from three sources in the following order:
1) RED +9.5 V dc while the RCU is turned on
2) the primary battery input while the RCU is in STBY
3) the hold up battery while the RCU is in STBY and the primary battery is removed
The ICOM power supply has switches that route transmit PT analog signals from the ICOM control module to the
two-wire interface for transmission, and that route receive PT analog signals from the bit sync switching module
to the ICOM control module. These lines are opened and the output to and input from the ICOM control module is
grounded when the RCU is operated in the CT mode.
The ICOM control module processes digital and TF data in all PT, CT, transmit, and receive modes. Digital data
rate selection is provided by the fill routing module via the asynchronous link with the control module. All low
speed data rates are interleaved up to 16 kb/s prior to transmission. This enables the receiver to use majority
logic error correction to improve bit error rate. In addition, PT digitalis exclusive ORed with a code word resulting
in a signal with a high transition rate that enables the receiver to track it more easily. A code word precedes the
digital transmission and tells the receiver that it is receiving digital data, that it is PT or CT, and when the actual
data starts. Low speed clocks are derived in this module from the 192-kHz clock from the main switching mod-
ule. A digital clock is sent to the AUD/DATA connector in both transmit and receive modes to clock data into and
out of the external data device. Transmit CT digital is first clocked into the ICOM control module by the low speed
clock, interleaved up to 16 kb/s, then clocked into the COMSEC module by a 16-kHz clock which it provides. The
COMSEC module encrypts the signal and outputs it on the transmit data CT (TDCT) line for transmission. In CT
receive modes the process is reversed. The received signal is decrypted by the COMSEC module and clocked
into the ICOM control by its 16-kHz clock. When the code words are detected, the signal is deinterleaved and
error corrected, then clocked out to the AUD/DATA connector by the low speed clock. The process for PT digital
is similar. The 16-kHz clock used in PT is provided by the main switching module. The incoming PT digital signal is
synchronized to this clock by the bit sync switching module as discussed in the control section.
12-7