8x930 Universal Serial Bus Controller Family

• Technology Overview
• Product Highlights
• Topology Overview
• Family Overview
• Production Description
• Architectural Overview
• Development Tools

Technology Overview
The Universal Serial Bus, or USB, brings Plug-and-Play technology to the external input and output devices found on today’s high-performance personal computers. USB brings with it three advanced features:

· Ease of use through hot plugging and automatic configuration
· Standardized connection points and simplified connector design
· Simple expansion through the use of a tiered-star hub topology

USB is motivated by the need to make the PC more user-friendly. The call to provide an inexpensive, standardized interface for today’s newest PC communications and I/O devices has allowed USB to emerge as a widely accepted industry standard. To date, more than 300 companies have joined the USB Implementer’s Forum (http://www.teleport.com/~usb) in support of this new interface.

The USB standard defines four transfer types in order to enable a variety of peripherals: Control, Isochronous, Interrupt and Bulk. Every peripheral must support control transfers for configuration, command, and status information flows. Isochronous transfers provide guaranteed bus access, constant data rate and error tolerance for devices such as CTI (computer-telephone integration) and audio systems. Interrupt transfers were designed to support human input devices such as joysticks, mice and keyboards that need to communicate small amounts of data infrequently, but with bounded service periods. Bulk transfers enable devices like printers, scanners, and digital cameras to communicate large amounts of data to the PC as bus bandwidth becomes available.

Topology Overview
The USB topology has three elements that work together to enable the four different transfer types: Host, Hub, and Function. Within a USB system, the host controls the flow of data and control information over the bus. This host capability is normally found on the PC motherboard, such as the integrated USB host found in Intel’s PCIset chip sets. Functions provide capabilities to the host system. These can include typical PC activities such as keyboard or joystick input and monitor controls, or more advanced activities like digital telephony and image transfer. The Intel 8x930Ax peripheral microcontroller is designed for function control. Finally, hubs provide an expansion point for USB by supplying a connection to other USB functions. The Intel 8x930Hx, which integrates USB function and hub control features, is the first production USB hub available for today’s PC peripheral devices.

USB hubs play an integral role in expanding the world of the PC user. With device connections furnished by embedded hubs in keyboards, monitors, printers, and other devices, attaching or removing a new peripheral is as simple as reaching for the plug. USB, featuring new levels of throughput and expanded connectivity sites could even bring about many new peripherals for the next generation of entertainment and productivity applications. Long gone are the days of add-in cards, IRQ conflicts, and knotted tangles of wiring.

For even simpler connectivity, the USB cable consists of only four wires: Vbus, D+, D-, and GND. A single standardized upstream connector type further increases the ease-of-use of USB peripherals. The data is differentially driven over D+ and D- at a bit rate of 12 Mb/s for full-speed signaling, or a rate of 1.5 Mb/s for the USB low-speed signaling mode. The USB-compliant 8x930 family has implemented the signaling transceiver on-chip, eliminating the need for all external circuitry, except for the pull-up terminating resistor on either the D+ or D- line to determine whether the device is full- or low-speed.

Family Overview
The Intel 8x930 family includes two different single chip Universal Serial Bus 1.0 specification-compliant controllers.

Intel’s 8x930Ax is an 8-bit controller designed specifically for USB peripherals and based on the MCS® 251 microcontroller architecture. The 8x930Hx, on the other hand, features the same time-proven MCS 251 microcontroller core, plus the advanced capability of an integrated USB hub controller. The MCS 251 architecture of both USB microcontrollers brings with it:

Code for the 8x930Ax and 8x930Hx can use either the MCS 51 or MCS 251 microcontroller instruction sets. This gives the user the option of protecting their software investment or gaining maximum performance in their application.

The 8x930 USB microcontrollers feature a rich combination of integrated peripherals that make them even more powerful. A Programmable Counter Array (PCA) provides the flexibility for applications that require real-time compare/capture, high speed I/O and pulse width modulation capabilities. Also included on both devices is an enhanced serial port, three 16-bit timer/counters, a hardware watchdog timer, four 8-bit I/O ports, and two power-saving modes: idle and power down.

Production Description
The 8x930 family has 1 Kbyte of on-chip data RAM and is available in ROMless, 8-Kbytes ROM, and 16-Kbytes ROM versions. These devices also have up to 256 Kbytes of external code/data memory space and 40 bytes of general purpose registers which reside in the CPU as register files. There are 16 possible byte registers, 16 possible word registers, and 10 possible Dword registers in the register file, depending on the combinations used.

Intel’s USB microcontroller family provides additional flexibility when interfacing to external memory. Designers have the option of utilizing up to 3 additional wait states or using the real time wait function to generate more wait states, which allows the use of slower memory devices. External instruction fetches can double performance by using Page mode to swap the data onto the high byte of the address.

Both microcontrollers in the 8x930 family have eight FIFOs (first in, first out) for internal downstream device support: four transmit FIFOs and four receive FIFOs. The four transmit/receive FIFOs support four function endpoints (0-3). Endpoint 0 is 16 bytes and is dedicated for control transfers. Endpoint 1 is user configurable up to 1024 bytes, and Endpoints 2 and 3 are each 16 bytes. These three endpoints can be used for interrupt, isochronous, or bulk transfer types. In the case of the 8x930Hx, these FIFOs are augmented by a FIFO pair for upstream communications. These endpoints are supported in the 8x930Hx by an additional Repeater unit, which is responsible for re-transmitting the data streams generated by downstream devices.

Architectural Overview
The implementation of USB on the 8x930Ax and 8x930Hx can be divided into four sections: FIFOs, Function Interface Unit, Serial Bus Interface Engine, and the Transceiver. The 8x930Hx has additional sections to control the additional hub functions, the Hub Interface Unit and the Repeater.

The transmit and receive FIFOs on both devices are circulating FIFOs supporting up to two separate data sets of variable sizes and containing byte count registers to access the number of bytes in the data sets. They also have flags that detect a full or empty FIFO and have the capability of re-transmitting or re-receiving the current data set. The Function Interface Unit (FIU) manages the USB data received and transmitted based on the transfer type and the state of the FIFOs. It is responsible for monitoring the transaction status, managing the FIFOs, and relaying control events to the 8x930 CPU via interrupt requests.

The Serial Bus Interface Engine (SIE) handles the communication protocol of USB by packet sequencing, signal generation/detection, CRC generation/checking, NRZI data encoding/decoding, bit-stuffing, and packet ID (PID) generation/decoding.

The integrated transceiver on Intel’s USB microcontrollers conforms to the simple four-wire interface defined by the USB 1.0 specification. The 8x930 family of controllers also have three interrupts associated with USB. These occur for any start of frame, transmit/receive done for function endpoints, and global suspend/resume. On the 8x930Hx hub device, the Hub Interface Unit (HIU) serves to control and manage the status of and communication to and from the downstream ports. The hub repeater, on the other hand, manages the propagation of signals in both directions for both the upstream and downstream USB ports.

Developement Tools
Intel’s USB product line is complemented by a complete set of hardware and software tools from Intel and leading third-party tool vendors. Software development is supported by ANSI C cross compiler, assembler, linker/locator, debugger, and simulators from Keil Software, Production Languages Corporation and Tasking BV. Device drivers and peripheral firmware development is supported by American Megatrends, Phoenix Technologies and SystemSoft Corporation. Hardware design and debug is supported by In-Circuit Emulators, and ROM Emulators from Nohau Corporation, Metalink Corporation and iSYSTEMS. Debugging the USB communication is supported by USB Protocol Analyzer tool from Computer Access Technology Corporation.

Evaluation of the 8x930 USB controller family is supported by the USB Evaluation Kit from Intel. This kit consists of a hardware evaluation board with upstream and downstream USB ports, documentation on the microcontroller and the board, ApBUILDER software, and evaluation C cross compiler tools from third-party vendors.