SparkFun Forums

[dumb]

Hi All,

I have following doubts, please clear it.

1) when a signal is considered as High Speed signal?
2) when impedance matching becomes more important? How to find such signals?
3) when routing, is it necessary to keep the length of the programming lines same on PCB always?

Thanks and regards

[jperch]

Wow,
These are some really general questions. But I will take a shot.

1) A signal is generally considered high speed when the frequencies contained in the signal either approach the limits of the circuitry carrying it or when the parameters of the circuitry significantly effect the signal. For example, when the wavelength of the frequencies in the signal get small enough to approach the physical dimensions of the circuitry, you will get some "signal integrity" issues begin to show up. These issues can be ringing or inflections in the rise/fall time of the signal.

2) Impedance matching becomes important when the signal is considered high speed (see number 1).

3) This depends on the timing requirements of the programming cycles. If the timing of the read/write cycle is sufficiently tight that signals are not arriving at the target device in time, then you should match line lengths. However, if the timing is loose enough that all the signals get where they need to be when they need to be there, or earlier, then you don't need to worry about matching line lengths.

I hope this is helpful,
Joe