Schematics the good
* Suitable for small design /stable products
Sure
* Quick
OK
* Easy to review & understand
Maybe -- it's just as easy to make a difficult-to-comprehend schematic as it
is an HDL file.
Maybe -- some tools convert schematics to HDLs prior to synthesis, in which
case there's arguably MORE chances for "hidden bugs" to creep in.
* Easy to go to lowest RTL level, WYSIWYG (if the tool has no bug
Another "maybe:" trying dropping down a schematic symbol for a multiplier and
compare the results to just using a multiply command in an HDL -- the bulk of
the result will be identical.
Schematics the bad
* Not suitable for big complex design
I wouldn't debate this personally, but playing devil's advocate: I'd say it
just takes *more effort* to do a "big, complex" design in schematics. They
were certainly done back before HDLs were available, after all.
* Difficulties for major upgrade/modification, remember your 1st grade
drawing skill?
It's not really "difficult," it's more just "slower" -- you have to re-draw a
lot.
* Hard copy & documentation
Possibly... if you archive everything as PDF it should be OK.
Schematic the ugly
* It looks ugly under the some hands, I mean it really ugly!
True, but as mentioned above, some people write really ugly HDL too.
* Not easy to migrate to other tools/devices
Here again I'd say "mainly slower" -- if you migrate from, e.g., Xilinx to
Altera, there's going to be a fair amount of design re-entry done (for a
complex design) regardless of the choice of HDL vs. schem.
* Take long design time for big & complex. Remember your first
schematic statemachine?
Yes, although for truly "big and complex" designs, the design entry time
should be small relative to the design, uh, design time itself. Of course,
I'd still prefer the shortest design entry time.
VHDL ? I would like to let others bring up the points
As I mentioned before, all contemporary tools support "mixed mode" design
entry, so you might as well let your engineers use whatever they're most
comfortable with so long as the results are well-organized and thus accessible
to others.
---Joel Kolstad