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|  MIL-N-81604C(AS)
Appendix I
30.5.12 CAU-CIU Interface
30.5.12.1 CAU-CIU Serial Interface - In the normal mode of
operation, the CAU receives CIU BCD display word data and
*
command word data via Data 2 under control of the CAU-ANCU
serial interface.
The CAU shall take control of this interface from the ANCU when
the CAU Control Command discrete from the ANCU to the CAU goes
*
to the true state as defined in 3.4.4.3.2b. The CIU shall
communicate with the CAU through line receivers and drivers in
the ANCU which shall remain operational even with the loss of
the internal ANCU power. Power from the CIU power source within
the ANCU shall be sufficient to maintain this CIU/CAU communica-
tions link. Digital data shall be transmitted between the CIU
and CAU in the backup modes (MAG SLV or FREE) consisting of
*
BCD data for right and left displays (magnetic variation and
latitude, respectively), a discrete data word for switch posi-
tions (command word), and a discrete data word for annunciator
*
lamps (status word). The electrical interface for signals
*
between units is Type A. Refer to 3.4.4.4 and 3.4.4.3.5.
CIU Clock - A 150-KHz clock with a pulse width
a.
of 833 ns shall be provided from the CAU to
the CIU.
Enter - This discrete pulse, which goes to
b.
its true state for two bit times when the CIU
ENTER pushbutton is depressed, shall be used to
initiate an address word to the CIU.
Control - This signal shall be a 28 clock
c.
period envelope sent from the CAU to CIU to
indicate to the CIU that serial data are to be *
taken in, sent out, or taken in and sent out.
The true state of this signal shall enable
serial transmission.
Serial Data from CAU to CIU - This data line
d.
shall transmit 8 bits of data (status or display
word) , LSB first, from the CAU. The status
word shall contain the bits which control the
ENTER, FREE, and MAG SLV lamps as well as the
sign and punctuation lamps for the left and
right display words. Each of these lamps shall
have one bit in the status word as specified
in table XI. There shall also be one data word *
assigned to each of the two display words
187
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