USB Electrical Characteristics
2
Figure 63 shows the I C bus timing.
SDA
202
203
204
208
205
207
SCL
206
209
210
211
Figure 63. I2C Bus Timing Diagram
14 USB Electrical Characteristics
This section provides the AC timings for the USB interface.
14.1 USB Interface AC Timing Specifications
The USB Port uses the transmit clock on SCC1. Table 30 lists the USB interface timings.
Table 30. USB Interface AC Timing Specifications
All Frequencies
Name
Characteristic
Unit
Min
Max
US1 USBCLK frequency of operation 1
MHz
MHz
Low speed
Full speed
6
48
US4 USBCLK duty cycle (measured at 1.5 V)
45
55
%
1 USBCLK accuracy should be ± 500 ppm or better. USBCLK may be stopped to conserve power.
15 FEC Electrical Characteristics
This section provides the AC electrical specifications for the fast Ethernet controller (FEC). Note that the timing
specifications for the MII signals are independent of system clock frequency (part speed designation). Also, MII
signals use TTL signal levels compatible with devices operating at either 5.0 V or 3.3 V.
15.1 MII and Reduced MII Receive Signal Timing
The receiver functions correctly up to a MII_RX_CLK maximum frequency of 25 MHz +1%. The reduced MII
(RMII) receiver functions correctly up to a RMII_REFCLK maximum frequency of 50 MHz + 1%. There is no
minimum frequency requirement. In addition, the processor clock frequency must exceed the MII_RX_CLK
frequency – 1%.
MPC875/MPC870 Hardware Specifications, Rev. 3.0
67
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
Freescale Semiconductor
FREESCALE [ Freescale ]
