TM 11-5820-890-30-4
12-10. DIGITAL DATA RECEIVE SIGNAL PATH. Continued
RCV CLK OUT, RCV DATA OUT, and SEQ DR DC OUT are inputs to the ICOM data I/O module. RCV CLK OUT is
input to a level shifter and output at +5 V and -5 V. The output of this level shifter is input to a switch controlled by
DGTL CLK OUT EN-N and Is switched to the AT/DDCO output when this control line is a logic 0. DGTL CLK OUT
EN-N is a logic 0 when 16K is selected, or when low speed data rates is selected and the code words have been
detected. RCV DATA OUT is inverted and input to a switch controlled by BLK ADMC-N. BLK ADMC-N is a logic 0
only when AD1 or TF data is received. The output of the switch is input to a line driver. The line driver level shifts
RCV DATA OUT to +5 V and -5 V when BLK ADMC-N is a logic 1, and provides a fixed level output for AD1 or TF
data when BLK ADMC-N is a logic 0. TF data is output at logic 0/1 levels on the SEQ OR DC OUT line. This digital
signal is low pass filtered and input to a switch which selects TF or AD1 for input to the line driver, AD2 SEL-N
controls this switch, selecting TF when it is a logic 0 and AD1 when it is a logic 1. AD1 is input to the ICOM data I/O
module on the RCV ANLQ/SIDETONE line and is input to the AD2 SEL-N switch immediately prior to the volume
control. The output of the driver is input to a switch controlled by DATA I/O EN and output on the AR/DDR line
when it is a logic 1. DATA I/O EN is a logic 0 when voice is received and is a logic 1 when TF, AD1, or digital data is
received.
12-11. DIGITAL DATA TRANSMIT SIGNAL PATH.
Digital data is clocked into the RCU from an external data device on the ADMC-N/DDT line (AUD/DATA pin F). See
figure FO-23. The clock output to the external device is provided by one of three sources. When data rates lower
than 16K (low speed data rates) are selected, the data rate adapter portion of the ICOM control module divides
its 192-kHz CLK/R input down to the appropriate rate. The low speed clock is routed to the ICOM data I/O module
on the RCV CLK OUT line. The ICOM data I/O module converts the logic 0/1 clock to +5 V/-5 V and routes the
clock out as DDCO when DGTL CLK OUT EN-N is a logic 0. DGTL CLK OUT EN-N is a logic 0 when a digital data rate
is selected, the data device has provided a PTT on the A/D PTT-N line, and the DDMC DET-N input to the ICOM
control module is a logic 0. External digital data devices ground AUD/DATA pin E (DDMC-N). DDMC-N iS detected
in the ICOM data I/O module and output as DDMC DET-N. DDMC DET-N is a logic 0 when DDMC-N is grounded,
and is a Iogic 1 when DDMC-N is open. When the 16K data rate is selected, RCV CLK OUT is provided from the
DDC output from the COMSEC module in CT and from the PT DGTL CLK/R output from the main switching module
in PT.
The digital data transmit (DOT) clocked in from the external device is converted from +5 V/-5 V to logic 0/1 levels
by the ICOM data I/O module and is output to the ICOM control module on the ADMC/DDT-N line. Low speed data
is routed to the data rate adapter portion of the ICOM control module. The data rate adapter interleaves, or
converts, the low speed data to 16 kb/s data and outputs this data to a code word generator. The code word
generator selects a PT or CT code word preamble and outputs it ahead of the converted 16K data. When PT Is
selected, the converted 16K data is also exclusive ORed with the code word prior to output. This exclusive OR
process ensures a high data transition rate, which makes it easier for the receiver to track. When CT is selected,
data is not exclusive ORed with the codeword. When the 16K data rate is selected, data is routed straight through
the ICOM control module, bypassing both the data rate adapter and the code word generator.
When PT is selected, the transmit digital data is output to the main switching module from the ICOM control
module, via the ICOM power supply, on the XMT PT DGTL/R line. In CT, the transmit digital data is output from the
ICOM control module to the COMSEC module on the DDT line. The COMSEC module encrypts the data and
outputs it to the main switching module on the TDCT line. The main switching module selects XMT PT DGTL in PT
(or TDCT in CT) for output to the two-wire interface on the PT/CT DGTL OUT line. The main switching module also
adds a phasing pattern to the beginning of PT digital transmissions. This phasing pattern allows the receiver to
detect and track the digital signal prior to the reception of actual data. When CT is selected, the COMSEC module
adds a phasing pattern to the data prior to output on the TDCT line, serving the same purpose. PT/CT DGTL OUT
is input to the two-wire interface, where it is FSK modulated onto the 40-kHz carrier for output on the 2-WIRE I/O
line. The control module monitors XMT DGTL MODE-N and RAD PTT-N to control the 40-kHz A/D SEL and 40-kHz
XMT ENBL lines, respectively. The control module places a logic 1 on the 40-kHz XMT ENBL line when RAD PTT-N
is a logic 0. RAD PTT-N is a logic 0 when the ICOM control module outputs an AUD MDL PTT-N/R, or when the
COMSEC module outputs a PTTR/PTTO.
12-18
