> Geoff,
> Does your suggested pairing mechanism only come into play for components
> which are placed on the back of the board or is it to be used elsewhere as
> well?
> Douglas McDonald

The pairing feature would primarily be provided for use with objects (arcs,
fills, pads, strings, or tracks) that are part of some component (so that
the Layer property of such objects automatically changes in an appropriate
manner when their parent component changes which side of the PCB it is on),
but would *also* be applicable (to some extent) to "free" objects (those
which are *not* part of some component). While the use of the L key (while
moving selected items or single components or other objects) is arguably
currently "broken" to some extent, any "free" object should still *also*
change which layer it is on, if it is on a Mechanical layer that has been
(user-)paired to another Mechanical layer, and the L key is pressed while it
is being moved (either by itself or as one of a number of objects that are
currently in a selected state).

In that regard, the paired Mechanical layers would behave like the existing
layers of a paired nature, to wit the Overlay, Paste Mask, Solder Mask, and
external signal (copper) layers.

Both "free" objects and non-"free" objects on such layers would also change
layers in the event that the *entire* PCB file was inverted, and regardless
of whether the inversion was of a Standard or Deep nature, and regardless of
whether the inversion was provided with Protel or implemented by an
user-provided addon server.

I also envisage that users could pair Mechanical layers on an "as-needed"
basis, so that up to eight pairs of paired Mechanical layers would be
available for those needing that many, while others would alternatively be
able to pair a smaller number of Mechanical layers, or even none at all.

The implementation could be simplified to some extent (with no loss in the
ability to control how many pairs of Mechanical layers are provided) by
restricting the pairing feature to "adjacent" Mech layers. As such, Mech 1
could be paired with Mech 2, but no other layer; similarly, Mech 3 could be
paired with Mech 4, but no other layer; ... ; Mech 15 could be paired with
Mech 16, but no other layer. And for each such pair of "adjacent" Mech
layers, the user could select whether those two layers actually are paired
to one another or not.

One way of implementing the associated user interface would be for the
"Setup Mechanical Layers" dialog box to incorporate another eight Checkboxes
(perhaps on a second Tab with a title of 'Pairing', but otherwise on the
existing 'Properties' Tab). One of those (new) Checkboxes would select (and
display) whether Mech 1 and Mech 2 are paired to one another or not, etc.

Conceptually, Mechanical layers could *presently* be paired to one another,
if an user-provided addon server was implemented which incorporated a
Process for controlling (and displaying) which layers are paired to one
another (details of which layers are thus paired could be retained, and
within the PCB file itself, by the use of Embedded objects, a feature
provided by Protel for use by developers), and one or more Processes for
updating the layer properties of objects on such layers as required. A
relatively recent post to this forum suggests that someone else actually has
done this (or at least some of those aspects). *However*, if a component is
moved to the opposite side of the PCB while using the L key (or invoking a
'Component' dialog box and then changing the 'Layer' property within that),
any objects within the component that are on Mech layers of a user-paired
nature will *not* have their Layer property appropriately updated at the
time (unless the addon server was clever enough to be able to monitor that
situation, and then arrange those properties to also be updated as required,
but that would be no small task to implement, assuming it could even be done
at all). And *that* is the reason why it would be desirable for this feature
to be built into Protel itself.

In more recent times, I suggested a couple of alternative options, such as
providing eight (or sixteen) entirely new layers which would provide four
(or eight) new "hard-wired" pairs of layers (for use *both* with components
*and* otherwise, as desired by each user), or else providing the user with
the ability to define new layers as desired (similar to Autocad and PCAD),
together with the ability to pair these to one another as desired (similar
to past versions of PCAD (and past/present versions of Autocad?)). In any
event, I strongly suspect that the existing four pairs of paired layers is a
source of frustration for at least some users, who would want to have more
such layers available for their use.

Geoff Harland.
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