is a separate assembly that is mounted to the Digital
Data Processing Group. Figure 7-8 is the functional
block diagram of the JTIDS terminal.
D I G I T A L D A T A P R O C E S S O R
GROUP. —The third drawer of the terminal houses
the digital data processor group. The two major
components are the interface unit (IU) and the
digital data processor (DDP). A battery assembly is
mounted to the front of the DDPG drawer. This
assembly consists of one nickel cadmium (NiCad)
battery and two lithium sulphur dioxide cells. The
NiCad battery will provide power to critical
components during short power failures. The lithium
sulphur dioxide cells supply power to the
chronometer.
The Interface Unit controls the communications
between the JTIDS terminal and the host computer
and provides amount for the Secure Data Unit (SDU).
On shipboard systems, the C2P is the host computer.
The Subscriber Interface Computer Program
(SICP) is a software program that controls the
communications with the host computer and provides
the data processing necessary to integrate the terminal
and the host computer. The IU and SICP also provide
the following functions: analog-to-digital and digital-
to-analog conversion of voice signals, feed through
interface between the DDP and the SDU, and primary
and backup power interface. The IU also provides the
interface for receiving and supplying the TACAN
blanking pulses. These blanking pulses prevent the
TACAN and the JTIDS terminal from transmitting at
the same time.
The Digital Data Processor (DDP) controls the
receiver/transmitter and the high-power amplifier
groups. The DDP performs the processing required
for transmitting and receiving Link-16 messages.
This processing includes the following:
Data encryption and decryption
Error detection and correction encoding and
decoding
Generation of the frequency-hopping pattern
Selection of the carrier frequency
Measurement of time of arrival data for
position and synchronization calculations
Figure 7-9.—The Digital Data Processing Group functional block diagram.
7-10
