Universal Serial Bus InterfaceMCF5253 Reference Manual, Rev. 1Freescale Semiconductor 24-4524.7 Functional DescriptionThe USB module can be broken down into functional sub-blocks described below.24.7.1 DMA EngineThe DMA Engine interfaces internally to dedicated DMA cache memory and has no access to mainmemory. It is responsible for moving all of the data to be transferred over the USB between the moduleand buffers in DMA cache memory. Like the system interface block the DMA engine block uses a simplesynchronous bus signaling protocol.16TXSTX endpoint stall. This bit will be set automatically upon receipt of a SETUP request if this Endpoint is not configuredas a Control Endpoint. It will be cleared automatically upon receipt of a SETUP request if this Endpoint is configuredas 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 continueto returning STALL until this bit is either cleared by the software or automatically cleared as above.1 Endpoint Stalled0 Endpoint OK15–8 Reserved.7RXERX endpoint enable.1 Enabled0 Disabled6RXRRX data toggle reset. Whenever a configuration event is received for this Endpoint, the software must write a one tothis bit in order to synchronize the data PID’s between the Host and device.5RXIRX data toggle inhibit. This bit is used for test only and should always be written as zero. Writing a one to this bit willcause this endpoint to ignore the data toggle sequence and always accept data packets regardless of their data PID.1 PID Sequencing Enabled0 PID Sequencing Disabled4 Reserved.3–2RXTRX endpoint type.00 Control01 Isochronous10 Bulk11 InterruptNote: When only one endpoint (RX or TX, but not both) of an endpoint pair is used, the unused endpoint should beconfigured as a bulk type endpoint.1RXDRX endpoint data sink. This bit should always be written as 0, which selects the Dual Port Memory/DMA Engine asthe sink.0RXSRX endpoint stall. This bit will be set automatically upon receipt of a SETUP request if this Endpoint is not configuredas a Control Endpoint. It will be cleared automatically upon receipt a SETUP request if this Endpoint is configured asa 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 continueto returning STALL until this bit is either cleared by the software or automatically cleared as above,1 Endpoint Stalled0 Endpoint OKTable 24-36. Endpoint Control 1 to 3 (ENDPTCTRLn) Register Field Descriptions (continued)Field Description
