MIL-DTL-24784 / 21B (SH)
names between units. Engineering schematics and cabling wire lists shall be used as the
source of signal names internal to a unit.
2. Power-on reset signals on the data FBDs shall be shown entering from external to the
function. No function block for power reset shall be shown on the data FBDs. The
generation of the power-on reset shall be shown on the power and grounding FBDs.
3. All signal lines between functional blocks on the FBDs shall be identified by descriptive
signal names. Signal lines that interface from one FBD sheet to another FBD sheet shall
have the identical signal name on each sheet. Signal lines that are identified on different
level FBDs (a signal level shown both on the primary FBD and on the secondary FBD)
shall be identified by the same signal name.
4. Reference designations shall not be used as signal names except in cases where no other
name exists.
5. The FBD number, sheet and zone shall be used to identify signal origins and destinations
when referencing from one FBD to another.
b.
Signal referencing for FBDs.
1.
Signal referencing on the same sheet. An on-sheet reference to show a continuous line
between two points shall be shown by a circle enclosing double capital letters with a lead
arrow indicating direction. Zone reference shall not be used (Letters to start with AA,
then AB, AC, and so forth). See figure 21-7.
a)
Signal lines shall show signal name on flow line before the reference symbol. See
figure 21-7.
b) An inverted triangle symbol shall not be used except for an A or B (primarily found
on the power FCDs) to indicate grounds.
2.
Signal referencing between two or more functional parts. To show a continuous line
between two points on different sheets of a functional breakdown (a function broken into
Parts 1 of 2, 2 of 2, and so forth), an irregular pentagon shall be used. Double capital
letters starting with BA then BB, BC, and so forth, shall be enclosed within this symbol.
Zone references shall be indicated. See figure 21-8.
3.
Signal referencing between functions. Referencing between units shown on the diagram
shall be accomplished at equivalent levels (that is, primary levels shall interface, second
levels shall interface; however, a primary level shall not interface with a second level).
See figure 21-9.
4.
Grouping of signals. Brackets may be used when all of a group of signals come from or
go to the same zone on destination. See figure 21-6.
c.
Diagram type. The diagram type (FBD or FCD) shall be included above the title block of the
drawing or on sheet 1 only. The title block shall appear only on sheet 1. Sheets 2 and on
shall not contain the diagram type block or the title block.
d.
Equipment names. Equipment name or reference designation shall be used to identify
hardware boundaries on the FBDs.
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