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Termination

The diagram below shows a high frequency square wave when observed with an analog scope:

Figure 3: Ringing

Clearly, if this signal were to be a clock-input to a device, there would be some serious problems. All signals used as clocks must be verified to see if termination is necessary. Inserting a resistor on the protoboard between the signal and ground can reduce this swing. A 100 resistor is ideal for most cases.

Note that with a 100 termination, the signal's logic high is now about 3.8 Volt, which satisfies the requirements of a TTL compatible device. If you feel the need to terminate a bus, ask the front desk for a resistor network. Its logic diagram is as follows:

Figure 4: Resistor Network