Information

Current
Endpoint
BDT
Buffer in Memory
BDT Page
Start of Buffer
•
000ODDINBDT_PAGE Registers END_POINT
• • • • •
End of Buffer
System Memory
Figure 40-3. Buffer descriptor table
40.3.2 RX vs. TX as a USB target device or USB host
The USB-FS core uses software control to switch between two modes of operation:
• USB target device
• USB hosts
In either mode, USB host or USB target device, the same data paths and buffer
descriptors are used for the transmission and reception of data. For this reason, a USB-FS
core centric nomenclature is used to describe the direction of the data transfer between
the USB-FS core and the USB:
• RX (or receive) describes transfers that move data from the USB to memory.
• TX (or transmit) describes transfers that move data from memory to the USB.
The following table shows how the data direction corresponds to the USB token type in
host and target device applications.
Table 40-1. Data direction for USB host or USB target
RX TX
Device OUT or Setup IN
Host IN OUT or SETUP
Chapter 40 Universal Serial Bus OTG Controller (USBOTG)
K20 Sub-Family Reference Manual, Rev. 2, Feb 2012
Freescale Semiconductor, Inc. 887