12-4
MCF5272 User’s Manual
Module Operation
12.2.1.1 USB Transceiver Interface
The USB module supports either an internal or external USB transceiver. USB_D+ and
USB_D- drive USB cable D+ and D- lines, respectively. With additional external protection
circuitry, equipment can be built that complies with Universal Serial Bus Specification,
Rev. 1.1. Transceiver performance specifications are described in the Chapter 7 of the
Universal Serial Bus Specification. See note on page , [p. 12-1].
When the internal transceiver is selected, (USBEPCTL0[AFEEN] is cleared), the driven
outputs can be observed by using the parallel port A if these pins are configured for USB,
using the PACNT register, 17.2.1, “Port A Control Register (PACNT)”.
The USB module has separate power pins for the internal transceiver.
NOTE:
USB_GND should always be grounded.
However, to reduce power consumption, USB_VDD may be left unconnected if either of
the following is true:
•
The USB module is not used.
•
An external transceiver is used.
12.2.1.2 Clock Generator
The USB module requires two clock inputs; the system clock and a 48-MHz data clock. The
data clock source is selectable between the USB_ExtCLK pin or the system clock. The
clock generator automatically uses the external clock as the data clock if it detects the
presence of a clock signal on the USB_CLK pin during system reset. This automatic
selection can be overridden by setting bit USBEPCTL0[CLK_SEL], Section 12.3.2.13. If
a clock signal is not present on USB_CLK, the clock generator uses the system clock.
NOTE:
In all cases, the system clock must be at least 24-MHz for the
USB module to function properly. If the system clock is used
for the USB data clock, the system clock frequency must be
48-MHz.
12.2.1.3 USB Control Logic
The control logic performs the following functions:
•
For transmitted data:
— Packet creation
— Parallel-to-serial conversion
— CRC generation
— NRZI encoding
— Bit stuffing
Содержание DigitalDNA ColdFire MCF5272
Страница 1: ...MCF5272UM D Rev 0 02 2001 MCF5272 ColdFire Integrated Microprocessor User s Manual ...
Страница 38: ...xxxviii MCF5272 User s Manual TABLES Table Number Title Page Number ...
Страница 58: ...1 10 MCF5272 User s Manual MCF5272 Specific Features ...
Страница 90: ...2 42 MCF5272 User s Manual Exception Processing Overview ...
Страница 96: ...3 6 MCF5272 User s Manual MAC Instruction Execution Timings ...
Страница 158: ...5 46 MCF5272 User s Manual Motorola Recommended BDM Pinout ...
Страница 184: ...7 12 MCF5272 User s Manual Interrupt Controller Registers ...
Страница 338: ...13 44 MCF5272 User s Manual Application Examples ...
Страница 414: ...18 6 MCF5272 User s Manual PWM Programming Model ...
Страница 452: ...19 38 MCF5272 User s Manual Power Supply Pins ...
Страница 482: ...20 30 MCF5272 User s Manual Reset Operation ...
Страница 492: ...21 10 MCF5272 User s Manual Non IEEE 1149 1 Operation ...
Страница 548: ...INDEX Index 12 MCF5272 User s Manual ...