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Universal Serial Bus Interface
MCF5253 Reference Manual, Rev. 1
Freescale Semiconductor
24-45
24.7
Functional Description
The USB module can be broken down into functional sub-blocks described below.
24.7.1
DMA Engine
The DMA Engine interfaces internally to dedicated DMA cache memory and has no access to main
memory. It is responsible for moving all of the data to be transferred over the USB between the module
and buffers in DMA cache memory. Like the system interface block the DMA engine block uses a simple
synchronous bus signaling protocol.
16
TXS
TX endpoint stall. This bit will be set automatically upon receipt of a SETUP request if this Endpoint is not configured
as a Control Endpoint. It will be cleared automatically upon receipt of a SETUP request if this Endpoint is configured
as a Control Endpoint.
The software can write a one to this bit to force the endpoint to return a STALL handshake to the Host. It will continue
to returning STALL until this bit is either cleared by the software or automatically cleared as above.
1 Endpoint Stalled
0 Endpoint OK
15–8
Reserved.
7
RXE
RX endpoint enable.
1 Enabled
0 Disabled
6
RXR
RX data toggle reset. Whenever a configuration event is received for this Endpoint, the software must write a one to
this bit in order to synchronize the data PID’s between the Host and device.
5
RXI
RX data toggle inhibit. This bit is used for test only and should always be written as zero. Writing a one to this bit will
cause this endpoint to ignore the data toggle sequence and always accept data packets regardless of their data PID.
1 PID Sequencing Enabled
0 PID Sequencing Disabled
4
Reserved.
3–2
RXT
RX endpoint type.
00 Control
01 Isochronous
10 Bulk
11 Interrupt
Note: When only one endpoint (RX or TX, but not both) of an endpoint pair is used, the unused endpoint should be
configured as a bulk type endpoint.
1
RXD
RX endpoint data sink. This bit should always be written as 0, which selects the Dual Port Memory/DMA Engine as
the sink.
0
RXS
RX endpoint stall. This bit will be set automatically upon receipt of a SETUP request if this Endpoint is not configured
as a Control Endpoint. It will be cleared automatically upon receipt a SETUP request if this Endpoint is configured as
a Control Endpoint,
The software can write a one to this bit to force the endpoint to return a STALL handshake to the Host. It will continue
to returning STALL until this bit is either cleared by the software or automatically cleared as above,
1 Endpoint Stalled
0 Endpoint OK
Table 24-36. Endpoint Control 1 to 3 (ENDPTCTRLn) Register Field Descriptions (continued)
Field
Description
Содержание MCF5253
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