MPC8280 datasheet(819/1386 Pages) FREESCALE

819 / 1386 page

Universal Serial Bus Controller

MPC8280 PowerQUICC II Family Reference Manual, Rev. 1

Freescale Semiconductor

27-3

Figure 27-1. USB Interface

The reference clock for the USB controller (USBCLK) is used by the DPLL circuitry to recover the bit

rate clock. The source for USBCLK is selected in CMXSCR[TS4CS] (refer to Section 16.4.3, “CMX SI2

Clock Route Register (CMXSI2CR)”). The MPC8280 can run at different frequencies, but the USB

reference clock must be four times the USB bit rate. Thus, USBCLK must be 48 MHz for a 12-Mbps

full-speed transfer or 6 MHz for a 1.5-Mbps low-speed transfer.

There are six I/O pins associated with the USB port. Their functionality is described in Table 27-1.

Additional control lines that might be needed by some transceivers (e.g., speed select, low power control)

may be supported by general purpose output lines.

Table 27-1. USB Pins Functions

Signal

I/O

Function

USBTXN,

USBTXP

Outputs from the USB transmitter, inputs to the differential driver

USBOE

Output enable. Enables the transceiver to send data on the bus.

USBTXP

USBRXD

D+

D–

USBOE

USBTXN

USBRXP

USBRXN

MPC8280

–

USB

transceiver

Result

Single ended “0”

Logic “0”

Logic “1”

—

MPC8280 Datasheet(PDF) 819 Page - Freescale Semiconductor, Inc