Hi Jorge,
I have designed my schematic in Eagle and I want to add despiking capacitors. They have to be close to the chip.
The manual is saying something about the INVOKE command, but not very clear? How do I add these small
despiking capacitors?
Please advise,
Very respectfully,
peter
(from The Hague Holland)
"People sometimes try to use 'lytics here, which is IMHO a mistake for high-speed circuitry. If you disagree with me, please be gentle, but they just, often, aren't fast enough."
No, I agree. Electrolytics tend to have a large inductive component, so are lousy for absorbing transition spikes which typically have frequency components that appear as high impedance at the inductance of a typical electrolytic.
"You can, if you have room, make helpful decouplers on a multi-layer board by using the power planes under the chip,"
I doubt there would be enough capacitance to make a difference in most cases.
"Supply traces should be thicker than signal traces, sometimes to the point of employing bus-bars."
Supply traces should be thick enough to deliver the peak current without critical voltage loss ["critical" is defined by the application]. Signal traces can, typically, be smaller [as most signals are conveyed with little or no current], but they don't have to be. They, can, in fact, be as large as the supply traces -- if there is room. And, in fact, this would come closer to satisfying the "don't etch copper unnecessarily" rule.
Decoupling is required on devices that generate current spikes when transitioning. The totem-pole outputs on TTL devices cause substantial current spikes because as they transition from 1 to 0 or vice-versa, there is a short period where both the upper and lower transistor is on, thus providing a low impedance path from supply to ground. This is less of an issue in CMOS devices -- and that's the extent of my knowledge--as I'm sure there is nuance in the many other logic families and such. The despiking capacitor must behave like a capacitor at the frequencies produced by the spike AND must store enough energy to supply enough current during the transition so that current isn't pulled from the supply line. The resistance path from the capacitor to the logic device must be low enough for the RC time constant to be faster than the frequencies involved AND the impedance through that same path must be low enough to allow the full spike current to flow from the capacitor to the IC AND the resonant frequency of the tank circuit created by the two series inductors created by the traces and the capacitance of the despiking capacitor must be much higher than the highest circuit frequency. This is why the despiking capacitor needs to be close to the logic device -- because the traces, like all wires, act like inductors and if too long, will have an inductance that presents a high impedance path between the capacitor and the logic device. And, in fact, ringing can occur, making the problem worse. Because the traces are inductors, they, in concert with the capacitor, produce a tank circuit.
I learned about the importance of despiking capacitors from the failure experienced by a friend of mine. He prototyped an elaborate TTL circuit and it acted nothing like what he intended. It had numerous counters that kept skipping counts and flip-flop states that kept transitioning when they shouldn't - it was a real mess.
This was back when TTL brand new and strange -- we hit the books and finally learned about despiking capacitors. After a liberal dusting, it started acting better, producing, nearly the intended result. Soon after that, we learned about synchronous counters -- heck we were just a couple of teenagers--what did we know 
100 mixed chips on a wirewrapped card
(remember the IC socketswith the 0.1ufd caps in them?
I remember them but luckily never had to work with them.
I do remember getting some nasty shocks poking around in there
I recall one of my fellow workers whom had grown used to 12v equipment, doing some leaping around as the high voltage got him ... 
When you talk about valves now some of them think you're bonkers .... why would you have a thing that stops air coming out in your electronics ...
I said in another post ...
people don't understand magic smoke .... even after you explain it doesn't work if you release it .... they still don't get it.
We should go back to valves so they can see where its held.
Mark
Ah the old days of 100 mixed chips on a wirewrapped card. We frantically
sprinkled 0.1ufd ceramic caps all over the place (remember the IC sockets
with the 0.1ufd caps in them?). Without proper bypassing, you could spend
weeks trying to troubleshoot a board only to discover the issue was
switching transients causing all your problems. Didn't have these issues
with vacuum tubes, but I do remember getting some nasty shocks poking
around in there 
mikey
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