In electronic circuit drawings there are two types of objects: component symbols and nets. Nets represent wires connecting the components – which represent physical devices. In a example bellow we see component type MAX3232. U2 is a reference label of component. Electronic component usually has pins. Pins always have their numbers starting from 1. Pins also have their names. They are usually written inside component block like C1+.
Fig1. Component Reading
For this particular component we used U2label. U (or IC) label applies to all semiconductors. But you know that resistors usually are labeled as R1, R3. Capacitors C1, C2, Diodes – D1, D2, Transistors Q1, Q2, Crystals – X1, X2, X3, Jumpers J1, J2, J3, Inductors L1, L2.
Other semiconductors devices may have special labels like RAM0, RAM1.
Fig2. Component Pins
Let’s go further and talk about PIN characteristics. In figure 2 we can see:
- Pin 1 – is a generic pin;
- Pin 2 has a bar over the name. This means that active is low signal;
- Pin 3 indicates that this is edge triggered input. Input responds on signal level change;
- Pin 4 and Pin 8 are GND and VCC (VDD). VCC stands for “collector†in other hand VDD stands for “drainâ€. This is just terminology both of them means voltages.
- Pin 7 is output-active high;
- Pin 6 is output active low;
- Pin 5 is labeled as NC – this means Not Connected.
Related signals may be routed using a bus wire.
Fig3. Routing using bus wires.
In figure 3 there is generic sub circuit, which can be used in many designs. You see that there are Ports used, that indicate the direction of signals. D0:D3 port is bidirectional, port A0:A3 is an output and port MODE is as input.
Fig4. Connected and not connected wires
In figure 4 there is shown how correctly wires should be drawn. If wires are interconnected, then dot should be drawn. Otherwise wires are just crossed, that means they are not connected.
Fig5. Variety of grounds
Always use ground symbols down and power source up.
thanks
Jamin