An analyzer tool plus in-circuit emulators (ICEs) are available for developing Universal Serial Bus (USB) interfaces based on variety of different USB-compliant controllers. Designed for monitoring USB communications, the USB Agent analyzer plugs into the USB line and simply connects via a parallel port to a PC serving as the protocol analyzer. A Windows user interface allows for control of the recording and viewing of the captured data.USB Agent can trigger the recording of USB communications either by an external signal or an internal “trigger condition”, or both. The external signal can come from one of the ICEs by triggering at a certain firmware condition, special routine, etc., or from a unit such as a logic analyzer. Emulation systems are available for USB controller chips made by Intel, Siemens, AMD, and other manufacturers.