In this final section, we will use a printer as an example to describe the requirements for USB-compliant devices. First, let's take a look at an outline of a legacy printer.

 

Outline of a legacy printer

 

If we were to add an USB interface without changing the system on the printer, we will need to develop a bridge.

 

Development of the bridge

 

As you can see, even a bridge for conversion to and from a USB interface will at the least require the development of a driver, firmware, and USB endpoints with controlling circuits.