PIC16LF1454 Datasheet, PDF (324/418 Pages) Microchip Technology – 14/20-Pin Flash, 8-Bit USB Microcontrollers with XLP Technology

PIC16(L)F1454/5/9
26.10 USB Operation Overview
This section presents some of the basic USB concepts
and useful information necessary to design a USB
device. Although a lot of information is provided in this
section, refer to the USB 2.0 specification for more
details, as needed.
26.10.1 LAYERED FRAMEWORK
USB device functionality is structured into a layered
framework, graphically shown in Figure 26-11. Each level
is associated with a functional level within the device. The
highest layer, other than the device, is the configuration. A
device may have multiple configurations. For example, a
particular device may have multiple power requirements
based on Self-Power Only or Bus Power Only modes.
For each configuration, there may be multiple
interfaces. Each interface could support a particular
mode of that configuration.
Below the interface is the endpoint(s). Data is directly
moved at this level. Endpoint 0 is always a control
endpoint and, by default, when the device is on the bus,
Endpoint 0 must be available to configure the device.
FIGURE 26-11: USB LAYERS
26.10.2 FRAMES
Information communicated on the bus is grouped into
1 ms time slots, referred to as frames. Each frame can
contain many transactions to various devices and
endpoints. Figure 26-7 shows an example of a
transaction within a frame.
26.10.3 TRANSFERS
There are four transfer types defined in the USB
specification:
Isochronous: This type provides a transfer method for
large amounts of data (up to 1023 bytes) with timely
delivery ensured; however, the data integrity is not
ensured. This is good for streaming applications where
small data loss is not critical, such as audio.
Bulk: This type of transfer method allows for large
amounts of data to be transferred with ensured data
integrity; however, the delivery timeliness is not
ensured.
Interrupt: This type of transfer provides for ensured
timely delivery for small blocks of data, plus data
integrity is ensured.
Control: This type provides device setup control.
While full-speed devices support all transfer types, low-
speed devices are limited to interrupt and control
transfers only.
Interface
Device
Configuration
To other Configurations (if any)
To other Interfaces (if any)
Interface
Endpoint Endpoint Endpoint
Endpoint Endpoint Endpoint
DS41639A-page 324
Preliminary
 2012 Microchip Technology Inc.