C541U_99 Datasheet, PDF (80/192 Pages) Siemens Semiconductor Group – 8-BIT CMOS MICROCONTROLLER

On-Chip Peripheral Components
C541U
6.4.1 Transfer Modes
USB data transfers take place between host software and a particular endpoint on a USB device. A
given USB device may support multiple data transfer endpoints. The USB host treats
communications with any endpoint of a USB device independently from any other endpoint. Such
associations between the host software and a USB device endpoint are called pipes. As an
example, a given USB device could have an endpoint supporting a pipe for transporting data to the
USB device and another endpoint supporting a pipe for transporting data from the USB device.
The USB architecture comprehends four basic types of data transfers.
Table 6-4
USB Transfer Modes
Mode
Control
Isochronous
(full speed
mode only)
Interrupt
Bulk
(full speed
mode only)
Function
Control data are used to configure devices, data transmission is lossless. Control
pipes are bidirectional, data transfer is possible in both directions via one pipe.
Endpoint 0 is always configured as control endpoint with a maximum buffer
length of 8 bytes. The control endpoint can be configured to handle data packets
of 64 bytes maximum length.
Isochronous data are continuous and real-time in creation and consumption,
such as voice data. In this case, real-time is defined from frame to frame.
Isochronous data transfer has the highest priority, but is not always lossless.
Isochronous pipes are always unidirectional, so one endpoint can be associated
to an IN pipe or an OUT pipe. The C541U supports up to 64 bytes.
Interrupt data are a small amount of data, which are transferred to the host every
n frames, with n being programmable by the host. Data delivery is lossless.
Interrupt pipes are always unidirectional IN pipes, the maximum data packet
length is limited to 64 bytes.
Bulk data can be a larger amount of data, which can be split by the host in several
data packets witin one frame. Data delivery is lossless.
Bulk pipes are always unidirectional, so one endpoint can be associated to an IN
pipe or an OUT pipe. The maximum data packet length is limited to 64 bytes.
Semiconductor Group
6-35
1999-04-01