The 8x931AA and 8x931HA USB peripheral controllers are based on the MCS51 microcontroller. They consist of standard 8XC51Fx peripherals plus a USB module. The 8x931HA USB module provides both USB hub and USB embedded function capabilities. The 8x931HA supports USB hub functionality, embedded function, suspend/resume modes, isochronous/non-isochronous transfers, and is USB rev 1.0 specification compliant. The USB module contains one internal and 4 external downstream ports and integrates the USB transceivers, serial bus interface engine (SIE), hub interface unit (HIU), function interface unit (FIU), and transmit/receive FIFOs. The 8x931AA is a hubless USB peripheral controller which contains the same feature set as the 8x931HA hub controller except for the hub module. The 8x931AA/HA uses the standard instruction set of the MCS 51 architecture.