The uPSD32xx family, from ST, consists of Flash programmable system devices with a 8032 Microcontroller Core. Of these, the uPSD3234A-40 and uPSD3254A-40 are notable for having a complete implementation of the USB hardware directly on the chip. This USB hardware complies with the Universal Serial Bus Specification Revision 1.1, and has a low-speed (1.5Mbit/s) device capability. Up to 8 bytes can be transmitted or received in one packet. The typical sustainable bus throughput is up to 6 KBytes per second on USB1.1, up to 11 KBytes per second with certain types of USB2.0 host.
There are times, such as to force a reset, when a physical USB device would be physically disconnected,and then reconnected. This application note presents a possible way of emulating, on demand by software,a disconnect of an embedded USB device, within the uPSD32xx, without needing to add any active components.