Pins

• Pins should all be 300 mils (3 grid spaces) long.
• For pins which are next to a logic bubble, make the pins 200 mils (2 grid spaces) long and then make the logic bubble 100 mils in diameter. In order to draw a 100 mil diameter circle, you will need to change the snap spacing to 50.
• A pin has two ends: one end has a red endpoint and one end that does not. The red endpoint is where nets can be connected. You can either rotate the pin so that this active end is in the right place or manually edit the symbol file changing the "whichend" parameter on the pin object. See the File Format document for more info.
• Be that all endpoints of pins which are meant to be connected to are on the 100 mil grid. The endpoint which is not active can be off the grid if necessary.
• Pins should be color number 1 (pins | white).
• Leave 400 mils (4 grid spaces) between (vertically) pins, unless you are drawing a special symbol, then just try to make it look good.
• Pin number attributes should be 50 mils above (or below; which ever makes the most sense) the pin which they are attached to.
• Input pins belong on the left and output pins belong on the right of the symbol.
• Please do not mix inputs and outputs on the same side of the symbol, unless absolutely necessary.
• You can have pins on the top or bottom of a symbol.
• The order for rows of pins (buses) should be LSB (least significant bit) to MSB (most significant bit). When drawing pins which are part of a bus, make sure the LSB of the bus is at the top (or for pins on top/bottom of a symbol, left of the rest of the other pins). Look at 74/74181-1.sym for a correct example of this order (A0 on top through A3 and B0 on top through B3). Violating this rule will make connecting buses much more difficult.
• When placing pins on logic gates, be sure to place the smallest pin numbers toward the top (or left) and then increment going down (or across).