Page 246 - The Art of Designing Embedded Systems

A Simple Drawing System 233

In addition, if the ECO is not immediately incorporated into the
drawing, the engineer issuing the ECO will mark the Master Drawing
Book with the ECO and a brief description of the reason for the ECO, as
follows:
Dwg # Title Revision Rev Date Filename
#3000 ProdABOM A 8- 1-97 PRODA-ASSY
ECO: PRODA.A.3 Stabilize clk PRODA.A.3
ECO: PR0DA.A. 1 Secure cables PR0DA.A. 1
Note that the filename of the ECO is included in the Master Drawing
Book.
When the ECO is incorporated into the drawing, remove the ECO an-
notation from the Master Drawing Book, as it is no longer applicable.
NEVER change a drawing without looking in the master repository
to see if other ECOs are outstanding against the drawing.
Every change gets an ECO, even if the change is immediately incor-
porated into a drawing. In this case, follow the procedure for obsoleting
a drawing. This provides a paper audit trail of changes, so we can see why a
change was made, and what the change was.
Every ECO will result in incrementing the version numbers of all af-
fected drawings. This includes the Configuration drawing as well. To keep
things simple, you do not have to issue an ECO to increment the Configu-
ration version number. We do want this incremented, though, so we can
track revision levels of the products. Add a line to the Master Drawing
Book listing the reason for the change and the new revision level of the
Configuration, as well as a list of affected drawings. This forms back
pointers to old drawings and versions. Though we remove old ECO history
from our drawings, never remove it from the Configuration drawing’s
Master Drawing Book entry, as this will show the product’s history.
The Master Drawing Book entry for an ECO’d Configuration draw-
ing will look like:

Dwg # Revision Rev date Title Filename
W600 A 8- 1-97 Prod A Configuration PRODA-ASSY
B 8-2-97 Mod clock circuit to be more stable
( 1OOO- 1, 1234 modified)
C 8-3-97 Secure cables better
Sometimes a proposed ECO may not be acceptable to production.
For example, a proposed mod may be better routed to different chip pins.
Therefore, the engineer making an ECO must consult with production