mc9s08jm16 Freescale Semiconductor, Inc, mc9s08jm16 Datasheet - Page 315

• Manufacturer Part Number: mc9s08jm16
• Description: S08jm 8-bit Usb Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

17.4.1.7
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
Freescale Semiconductor
summarizes the differences in enabling the USBDP pullup for different USB power modes.
USB Powering and USBDP Pullup Enable Options
Figure 17-18. USBDP/USBDN Pullup Resistor Configuration for USB module
Bus Power
(Built-in VBUS sense)
Self Power
(Build VBUS sense into application)
Table 17-20. USBDP Pullup Enable for Different USB Power Modes
3.3 V
Power
R
DPPU
MC9S08JM16 Series Data Sheet, Rev. 2
USBDP Pullup
External
External
Internal
Internal
V
USBDP
USBDN
USB33
Universal Serial Bus Device Controller (S08USBV1)
USB DEVICE
Build into application
Build into application
Pullup Enable
Set USBPU bit
Set USBPU bit
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