All devices come preprogrammed with the USB BSL. Use of the USB BSL requires external access to six pins (see Table 9-5). In addition to these pins, the application must support external components necessary for normal USB operation; for example, the proper crystal on XT2IN and XT2OUT or proper decoupling.
|DEVICE SIGNAL||BSL FUNCTION|
|RST/NMI/SBWTDIO||Entry sequence signal|
|PU.0/DP||USB data terminal DP|
|PU.1/DM||USB data terminal DM|
|PUR||USB pullup resistor terminal|
|VBUS||USB bus power supply|
|VSSU||USB ground supply|
The default USB BSL evaluates the logic level of the PUR pin after a BOR reset. If the PUR pin is pulled high externally, the BSL is invoked. Therefore, unless the application is invoking the BSL, it is important to keep PUR pulled low after a BOR reset, even if BSL or USB is never used. TI recommends applying a 1-MΩ resistor to ground.