MC9S08JM16 Datasheet, PDF (313/386 Pages) Freescale Semiconductor, Inc – Microcontrollers

Universal Serial Bus Device Controller (S08USBV1)
• Bit stuffing violation
If a properly formatted packet is received, the receiver logic initiates a handshake response to the host. If
the packet is not decoded correctly due to bit stuff violation, CRC error or other packet level problem, the
receiver ignores it. The USB host will eventually time-out waiting for a response, and retransmit the
packet.
When the SIE receiver logic is receiving data in the buffer space for a particular endpoint, CPU access to
that buffer space is not recommended.
17.4.1.2 MCU/Memory Interfaces
17.4.1.2.1 SkyBlue Gasket
The SkyBlue gasket connects the USB module to the SoC internal peripheral bus. The gasket maps
accesses to the endpoint buffer descriptors or the endpoint buffers into the shared RAM block, and it also
maps accesses to the peripherals register set into the serial interface engine (SIE) register space. The
SkyBlue gasket interface includes registers to control the USB transceiver and voltage regulator.
17.4.1.2.2 Endpoint Buffer Manager
Each endpoint supported by the USB device transmits data to and from buffers stored in the shared buffer
memory. The serial interface engine (SIE) uses a table of descriptors, the Buffer Descriptor Table (BDT),
which is also stored in the USB RAM to describe the characteristics of each endpoint. The endpoint buffer
manager is responsible for mapping requests to access endpoint buffer descriptors into physical addresses
within the USB RAM block.
17.4.1.2.3 RAM Arbitration
The arbitration block allows access to the USB RAM block from the SkyBlue gasket block and from the
SIE.
17.4.1.3 USB RAM
The USB module includes 256 bytes of high speed RAM, accessible by the USB serial interface engine
(SIE) and the CPU. The USB RAM runs at twice the speed of the bus clock to allow interleaved
non-blocked access by the CPU and SIE. The USB RAM is used for storage of the buffer descriptor table
(BDT) and endpoint buffers. USB RAM that is not allocated for the BDT and endpoint buffers can be used
as system memory. If the USB module is not enabled, then the entire USB RAM may be used as unsecured
system memory.
17.4.1.4 USB Transceiver (XCVR)
The USB transceiver is electrically compliant to the Universal Serial Bus Specification 2.0. This block
provides the necessary 2-wire differential NRZI signaling for USB communication. The transceiver is
on-chip to provide a cost effective single chip USB peripheral solution.
MC9S08JM16 Series Data Sheet, Rev. 2
Freescale Semiconductor
313