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Page Title:
Command and message format definition. |
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|  MIL-D-70789A (AR)
shall have the following characteristics:
a. The prime system shall be the bus master which
initiates commands to the DRU (slave). The DRU shall respond to
commands within 10 seconds after application of power.
The DRU shall not initiate a message without a
b.
request (command).
The DRU shall send a message in response to each
c.
command received. The message shall be returned only on the bus
over which the command was received.
STATUS (30.5) and ALERT (30.4.6) indications
d.
applicable to only one data bus (i.e. improper command received,
error detected, etc.) shall be returned only on the applicable
bus.
Commands and messages shall be constructed of 8-bit
bytes (designated as characters).
The data field shall be constructed of a variable
f.
number of characters from a minimum of zero to a maximum of N.
All other fields are of fixed character length.
Bit positions within a character are shown below:
g.
least
most
significant
significant
bit
bit
7654
3
2
1
0
The order of transmission" over the bus shall be most
h.
significant character (8 bit byte) first. The last significant
bit within the character shall be transmitted first. In multiple
or single character data words which do not assign all of the
bits available, the least significant bit or bits within the
least significant character shall be the unassigned bit or bits.
The value(s) of unassigned bit(s) are unspecified.
Command and message format definition.
Command
3.5.4.4.3.1
and message formats are shown below:
F
E1 E2
D1 D2. . . . . . . ..DN
C
F
INPUT COMMAND TO DRU
F
El E2
D1 D2 . . . . DN
S1 S2
I
F
OUTPUT MESSAGE FROM DRU
30
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