Universal Serial Bus (USB)
18-16
Am186™CC/CH/CU Microcontrollers User’s Manual
stop the hardware, requiring device software to take appropriate action and then clear
the ACT_REQ bit to let the hardware continue.
– Perform any additional programming of the definition registers that is required for the
specific application.
2. In the General-Purpose DMA Control 0 (GDxCON0) register for an available general-
purpose DMA channel, set DSEL = 11101b (USB Endpoint C, destination
synchronized). Make any other DMA channel configuration settings that are required,
then set ST = 1 in the GDxCON0 register to enable the DMA channel. Enable the DMA
channel before enabling the DMA request source to avoid data loss or initial error
conditions.
It is important to note that in DMA mode, the ACT_REQ bit no longer serves as a
semaphore lock for the data FIFO. The data FIFO now behaves as a circular FIFO with
simultaneous read/write capability. The ACT_REQ bit acts as a Stop/Go bit for the
hardware. For details, see the xEPCTL register description in the
Am186™CC/CH/CU
Microcontrollers Register Set Manual, order #21916. If software sets the endpoint’s
ACT_REQ bit, the DMA transfer stops until software clears the bit again.
18.5.2
Data Transmission and Data Types
For the Am186CC and Am186CU microcontrollers, all communication across the USB takes
place in Full-speed mode. USB bus transactions involve transmissions in up to three types
of packets: token, data, and handshake. The token packet contains information about the
type and direction of the transaction as well as the device address and which endpoint to
use. The data packet, if any, contains actual commands or data. There can be one data
packet, none, or more than one in a transaction. The format of a data packet varies according
to what type of endpoint is being used. The handshake packet contains information
regarding whether or not the transaction was completed successfully.
When beginning a transfer, the host issues a start-of-frame (SOF) packet. When the USB
peripheral controller decodes this packet, it indicates the start-of-frame in the USB Interrupt
Status 2 (UISTAT2) register. Also decoded in the start-of-frame packet is a time stamp,
which the USB peripheral controller places in the Time Stamp (TSTMP) register.
18.5.2.1
USB Suspend, Resume, and Remote Wakeup
A USB Suspend is indicated if traffic across the USB cable ceases for 3 ms or more. This
causes the USB peripheral controller to go into Suspend mode, which hardware indicates
by setting both the SUSP bit in the USB Device Miscellaneous Functions (USBMFR) register
and the USB_SUS bit in the USB Interrupt Status 2 (UISTAT2) register. The USB_SUS can
be enabled as an interrupt source by setting the corresponding bit in the UIMASK2 register.
When a USB Suspend is detected, software should take any necessary action and wait for
a USB Resume, which hardware indicates by clearing the SUSP bit in the USBMFR register
and by setting the USB_RES bit in the UISTAT2 register. USB_RES can also be enabled
as an interrupt source by setting the corresponding bit in the UIMASK2 register.
The Remote Wakeup feature is provided for peripheral devices that might need to wake up
the USB remotely. The device’s Remote Wakeup feature must be enabled by the host,
which does so by issuing an appropriate SET_FEATURE command to the device. This
automatically sets the RWAKE_EN bit in the USBMFR register.
If the RWAKE_EN bit is set and the controller is in USB Suspend mode, device software
can initiate a USB Resume by setting the RWAKE bit in the USBMFR register.
Содержание Am186 CC
Страница 1: ...Am186 CC CH CU Microcontrollers User s Manual Order 21914B...
Страница 4: ...iv Am186 CC CH CU Microcontrollers User s Manual...
Страница 18: ...Table of Contents xviii Am186 CC CH CU Microcontrollers User s Manual...
Страница 24: ...Introduction xxiv Am186 CC CH CU Microcontrollers User s Manual...
Страница 39: ...Architectural Overview Am186 CC CH CU Microcontrollers User s Manual 1 15 Figure 1 6 32 Channel Linecard CH CC...
Страница 40: ...Architectural Overview 1 16 Am186 CC CH CU Microcontrollers User s Manual...
Страница 86: ...System Overview 3 36 Am186 CC CH CU Microcontrollers User s Manual...
Страница 92: ...Emulator Support 4 6 Am186 CC CH CU Microcontrollers User s Manual...
Страница 112: ...DRAM Controller 6 8 Am186 CC CH CU Microcontrollers User s Manual...
Страница 134: ...Interrupts 7 22 Am186 CC CH CU Microcontrollers User s Manual...
Страница 186: ...Programmable I O Signals 9 8 Am186 CC CH CU Microcontrollers User s Manual...
Страница 200: ...Watchdog Timer 11 6 Am186 CC CH CU Microcontrollers User s Manual...
Страница 232: ...Asynchronous Serial Ports UARTs 13 24 Am186 CC CH CU Microcontrollers User s Manual...
Страница 242: ...Synchronous Serial Port SSI 14 10 Am186 CC CH CU Microcontrollers User s Manual...
Страница 264: ...High Level Data Link Control HDLC 15 22 Am186 CC CH CU Microcontrollers User s Manual...
Страница 332: ...Universal Serial Bus USB 18 34 Am186 CC CH CU Microcontrollers User s Manual...
Страница 348: ...Register Summary A 16 Am186 CC CH CU Microcontrollers User s Manual...
Страница 376: ...Index Index 18 Am186 CC CH CU Microcontrollers User s Manual...