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

A while ago, there was a longer thread in this forum dealing with EMI problems, see [url]http://forums.parallax.com/forums/default.aspx?f=7[/url]. The methods that help to keep radiation from the SX to the outside low are also good to keep external noise going into the SX low.

I'm using the SX 28 in applications where DC motors (24V, 18Amps) and various releays are turned on and off without trouble. The SX 28 is sitting on a separate small multi-layer board with two inner layers, one connected to Vdd, and the other to Vss. I have measured a capacity of about 1 nF between the Vdd an Vss terminals on an empty PCB. This capacity is caused by the two inner supply layers, and it is almost an ideal capacitor as it has ony very little parasitic series inductance. This board passed EMI approval with no problems, i.e. the radiated RF signals were below the limits, and the board could stand external bursts and spikes without abnormal operation.

Once having made this experience, I now design all my PCBs for commercial applications with two inner supply layers. Today, such boards are not much more expensive than double-sided ones.

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