Freescale Semiconductor PowerQUICC MPC885 Reference Manual page 851

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 SICR, see
(SICR)." The MPC885 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
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.
Signal I/O
USBTXN, O Outputs from the USB transmitter, inputs to the differential driver.
USBTXP
USBOE O Output enable. Enables the transceiver to send data on the bus.
Freescale Semiconductor
MPC885
USBOE
USBTXP
USBTXN
USBRXD
USBRXP
USBRXN
Figure 31-1. USB Interface
Table 31-1. USB Pins Functions
.
TP
0
0
1
1
MPC885 PowerQUICC Family Reference Manual, Rev. 2
USB
transceiver
D+
D-
+
–
Section 20.2.4.3, "SI Clock Route Register
Function
TN Result
0 single ended "0"
1 logic "0"
0 logic "1"
1 —
Universal Serial Bus (USB)
Table 31-1.
31-3