In SX Microcontrollers, SX/B Compiler and SX-Key Tool, g_daubach wrote:

William,

I partly agree with Paul. He is right, in general the datasheet describes the specifications of a component and not necessarily its applications. On the other hand, a special note in the datasheet that due to their high speeds, SX controllers require specific attention concerning EMI, and supply bypassing would be appropriate, or at least a reference to the EMI app note.

I know that Parallax is in a state of revising all SX datasheets, so there now is a good chance for adding such information. Rocklin - did you copy? :-) .

Somehow, I feel like a missonary, preaching the four-layer PCB design. With the two inner supply layers, you would not have a problem, connecting all Vdd/Vss pins of the SX48/52, still leaving you enough real estate for other signal traces.

I have designed a general-purpose board for the SX28 that I call the "SX-Multi Board". Although the two inner layers look like Swiss Cheese due to the many plated-through holes for the breadboarding sections, the two inner layers build up a capacity of about 1 nF. This sounds like a pretty small value but as this is an almost ideal bypass capacitor it is more effective than a discrete bypass capacitor placed somewhere on the board. A good (bad?) example where the bypass capacitor should _NOT_ sit is the SX-Tech board. It is placed "miles away" from the Vdd and Vss pins at the left small side of the ZIF socket. Would not be a problem placing it much closer to pins 2 and 4 for better filtering. OK, the SX-Tech board is an experimental tool, not designed for commercial applications. I bet - it would fail any EMI test.

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