MC9S08JM16 Datasheet, PDF (315/386 Pages) Freescale Semiconductor, Inc – Microcontrollers

Universal Serial Bus Device Controller (S08USBV1)
USB DEVICE
3.3 V
R_DPPU
V_USB33
USBDP
USBDN
Figure 17-18. USBDP/USBDN Pullup Resistor Configuration for USB module
17.4.1.7 USB Powering and USBDP Pullup Enable Options
The USB module provides a single-chip solution for USB device applications that are self-powered or
bus-powered. The USB device needs to know when it has a valid USB connection in order to enable or
disable the pullup resistor on the USBDP line. For the USB module on this device, the pullup on USBDP
is only applied when a valid VBUS connection is sensed, as required by the USB specification.
In bus-powered applications, system power must be derived from VBUS. Because VBUS is only available
when a valid USB connection from host to device is made, the VBUS sensing is built-in, and the USBDP
pullup can be enabled accordingly.
With self-powered applications, determining when a valid USB connection is made is different from that
of bus-powered applications. In self-powered applications, VBUS sensing must be built into the
application. For instance, a KBI pin interrupt can be utilized (if available). When a valid VBUS connection
is made, the KBI interrupt can notify the application that a valid USB connection is available, and the
internal pullup resistor can be enabled using the USBPU bit. If an external pullup resistor is used instead
of the internal one, the VBUS sensing mechanism must be included in the system design.
Table 17-20 summarizes the differences in enabling the USBDP pullup for different USB power modes.
Table 17-20. USBDP Pullup Enable for Different USB Power Modes
Power
Bus Power
(Built-in VBUS sense)
Self Power
(Build VBUS sense into application)
USBDP Pullup
Internal
External
Internal
External
Pullup Enable
Set USBPU bit
Build into application
Set USBPU bit
Build into application
MC9S08JM16 Series Data Sheet, Rev. 2
Freescale Semiconductor
315