Configuring Gates

Once you have drawn, say, a capacitor, you may wonder what its capacitance is, and how to set the capacitance you want. The way to do this is called configuration.

Each kind of gate has a set of attributes, usually numbers, that tell more specifically what kind of circuit element it is. For example, AnaLOG capacitors have a "capacitance" attribute, and transistors have a hatfull of attributes about width/length, kT/q, parasitic capacitances, etc.

In the digital world, most gates do not have attributes. An exception is the clock generator, CLOCK, which you can configure to control the clock frequency and waveform. Also, many digital gates have text on their attribute screens that describes how to use the gate.

Exploring Configuration Mode

In the lower-right corner of the screen is the word ROT with a curving arrow. This tells Log that when you tap a gate, it should rotate it by 90 degrees. If you press the word ROT, it changes to MIR. Now if you tap a gate it mirrors itself left-to-right. Pressing MIR leads to MIR with a bar (up-down mirroring), then to CNFG in yellow, then back to ROT. If you tap a gate while in CNFG mode, instead of reorienting it you open it up for configuration.

When a gate is open for configuration, its attributes are displayed. Notice that of the attributes is highlighted. To highlight a different attribute, press the up- and down-arrow keys. To enter a new value for an attribute, highlight it, then just type in the value you desire.

Some attributes can have scale factors, e.g., "m" for milli- and "u" for micro-. These will show up as, say, "1.2mV", meaning 1.2 millivolts. When you type a new value, you can always leave off the V since that part is obvious, but don't forget to include the "m" if that's what you want! A common mistake is to change 20pA to 30A, thus seriously perturbing the operation of the simulated circuit. When in doubt, you can always type scientific notation in "1.2E-4" format.

Some attributes are choices instead of numbers. For example, voltage sources let you choose a waveform of either "DC," "Pulse," or "Sine." You can type whole words to change these attributes, or use the arrow keys to cycle through the choices.

To return an attribute to its default value, just press Enter all by itself on that line. Some attributes can be blank, in which case whatever feature they correspond to is disabled. Others must have values, and Log will use some default if you try to enter "blank."

To finish configuring a gate, press the right mouse button again, or hit Control-C.

john [dot] lazzaro [at] gmail [dot] com