Datasheet

Universal Serial Bus Device Controller (S08USBV1)

MC9S08JM60 Series Data Sheet, Rev. 3

Freescale Semiconductor 315

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 USBDP Pullup Pullup Enable

Bus Power

(Built-in VBUS sense)

Internal Set USBPU bit

External Build into application

Self Power

(Build VBUS sense into application)

Internal Set USBPU bit

External Build into application

USBDP

USBDN

USB DEVICE

USB33

3.3 V

DPPU