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Appendix A: Huds Signal Interface |
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|  MIL-S-70442 (AR)
APPENDIX
A
HUDS SIGNAL INTERFACE
REQUIREMENTS
Detail characteristics. The HUD communicates with the Fire
Control Computer (FCC), the TOW Missile System (TMS), the AN/APM 209
radar altimeter, Airborne Laser Tracker (ALT), and the Laser Range
Data transmission from the FCC and from the LRF is by
Finder (LRF).
means of dedicated serial-data busses. Signals from the TMS and the
radar altimeter are in the form of parallel discrete and analog
signals.
HUD-FCC interface. The FCC transmits data to HUD by means of
dedicated serial digital bus. The line consists of a twisted,
shielded wire pair which carries the data and its logical
complement. The wiring configuration is shown in Figure 14. A
timing diagram illustrating typical signal timing is shown in Figure
15.
Bus characteristics. The data line-pair between the FCC and the
HUD consists of a twisted shielded wire pair with a characteristic
impedance of 71 ohms, + 10 percent. The shield on this pair is
grounded in accordance with good EMI suppression practices. Data is
transmitted and received by differential 3-state logic transmitters
and receivers. The signal levels used shall be TTL compatible.
Data format. The data is sent asynchronously at a normal 9600
bit/second rate. Each data byte forms a part of an 11-bit
transmission period consisting of a start bit, 8-bit data byte, stop
bit, and parity bit, as shown in the timing diagrams of Figure 15.
Transmitted parity, including parity bit, is odd. Two such bytes
sent sequentially make up a 16-bit word.
Message format. The information sent in the data words are in
the sequence shown in Table I. The FCC sends all six words, two
bytes per word, each data transmission.
HUD-LRF interface. The LRF transmits data to the HUDS on a
serial digital data bus like that for the FCC. The wiring
configuration is as shown in Figure 14. In the event of FCC
failure, data transmission is to be received directly from the LRF
with signal timing as shown in Figure 16.
HUD-TMS
interface.
The HUDS replaces the Pilot's Steering
Indicator (PSI) in the TMS and so receives all the signal
information which the PSI would normally receive.
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