block diagram

Boxes for components, labeled lines for what passes between them, and a small square where each line meets a box. Draw a dashed edge around the boxes you are treating as inside, and every crossing becomes an interface you can name. This is the plain version and the one to start with. Its whole value is that it makes you write a noun on every line, and a line you cannot label is a connection you have not thought about yet.

Boxes for components, labeled lines for what passes between them, and a small square where each line meets a box. Draw a dashed edge around the boxes you are treating as inside, and every crossing becomes an interface you can name. This is the plain version and the one to start with. Its whole value is that it makes you write a noun on every line, and a line you cannot label is a connection you have not thought about yet.

Example

Best when you can name the parts and want to force yourself to say what actually passes between them.