10 MPC885/MPC880 PowerQUICC™ Family Technical Summary MOTOROLA
PRELIMINARY—SUBJECT TO CHANGE WITHOUT NOTICE
Universal Serial Bus (USB) Universal Serial Bus (USB)
The implementation of bursting DMA reduces bus usage. Independent DMA channels for accessing BDs
and transmit and receive data minimize latency and FIFO depth requirements.
T ransmit and receiv e FIFOs further reduce bus usage by localizin g all collisions to the FEC. T ransmit FI FOs
maintain a full collision window of transmit frame data, eliminating the need for repeated DMA over the
system bus when collisions occ ur . On the r eceive side, a full collision wi ndow of data is recei ved before any
receive data is transferred into system memory, allowing the FIFO to be flushed in the event of a runt or
collid ed fram e, with no DMA activi ty. However, external memory for buf fer s and BDs is requi red; on- chip
FIFO s are desi gned only t o compens ate fo r collisions an d system bus la tency.
Independent TxBD and RxBD rings in external memory allow nearly unlimited flexibility in memory
management of transmit and receive data frames. External memory is inexpensive, and because BD rings
in external memory have no inherent size limitations, memory management can be easily optimized to
system needs.
8 Universal Serial Bus (USB)
The univ ersal serial bus (USB) is an indus try-standar d extension to the PC archite cture. The USB control ler
on the MPC885 family supports data exchange between a wide range of simultaneously accessible
peripherals. Attached peripherals share USB bandwidth through a host-scheduled, token-based protocol.
The USB physical interconnect is a tiered-star topology, and the center of each star is a hub. Each wire
segment is a point-to-poin t connection betwee n the host and a hub or func tion, or a hub connected to another
hub or a f unction. T he USB transf ers sign al and power over a fou r- wire cable , and t he signali ng occurs over
two wires and point-to-point segments. The USB full-speed signaling bit rate is 12 Mbps. Also, a limited
capability low-speed signaling mode is defined at 1.5 Mbps. Refer to revisions 1.1 and 2.0 of the USB
Specification for fu rther deta ils. They c an be downloaded from http:/ /www. usb.org.
The MPC885 USB controller consists of a transmitter module, receiver module, and two protocol state
machines. The protocol state machines control the receiver and transmitter modules. One state machine
implements the func tion state diagram, and the other implements the host state diag ram. The USB controller
can implement a USB function endpoint, a USB host, or both for testing purposes (loopback diagnostics).
9 Communications Processor Module (CPM)
The MPC885 family is the next generation MPC8xx family of devices. Like its predecessor it implements
a dual-processor architecture, which provides both a high-performance, general-purpose processor for
applica tion programming us e and a special-p urpose communication proce ssor (CPM) uniquely designed for
communications applications.
The CPM contai ns feature s that, like its pre decessor, allow the MPC885 family to exc el in communicat ions
and networking products. These features are grouped as follows:
• Communications processor (CP)
• Independent DMA (SDMA) controllers
• Four general-purpose timers
The CP provides the communication features of the MPC885 family. Included are a RISC processor, three
serial communication controllers (SCCs), two serial management controllers (SMCs), a serial peripheral
interface (SPI), an I2C interface, 8 Kbytes of dual-port RAM, an interrupt controller, a time-slot assigner
(TSA), five parallel ports, a parallel interface port, four independent baud rate generators, and serial DMA
channels to support the SCCs, SMCs, SPI, and I2C.
Freescale Semiconductor, I
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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