Inside the peripheral

The Intel 8x930Ax USB Peripheral Controller (Product Brief, Data Sheet) incorporates USB features while offering a combination of high performance, ample memory mix and addressing, low power, low noise, efficient high-level language support, an enhanced instruction set, integrated features and functionality.

The USB cable contains only four wires: Vbus, D+, D- and GND. Data is differentially driven over D+ and D- at a full-speed signal rate of 12 Mb/second or a low-speed rate of 1.5 Mb/second. The transceiver is built on-chip with no external circuitry needed, except for the pull-up terminating resistor on either the D+ or D- line to select a full-speed or low-speed device.

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

The FIU manages USB data that is received and transmitted based on the transfer type and state of the FIFOs. It monitors the transaction status, manages the FIFOs and relays control events to the 8x930Ax CPU via interrupt requests.

The 8x930Ax USB Controller has a total of eight FIFOs (first-in/first-out): four transmit FIFOs and four receive FIFOs. The transmit/receive FIFOs support four function endpoints (0-3). Endpoint 0 is 16 bytes and is dedicated for control transfers. Endpoint 1 is configurable up to 1,024 bytes, and endpoints 2 and 3 are each 16 bytes. These endpoints can be used for interrupt, isochronous or bulk transfers.

Firmware is the interface between USB and the user application code. The 8x930Ax USB Controller may be programmed using either the Intel MCS® 51 instruction set (to protect the user's software investment) or the MCS® 251 microcontroller instruction set (for optimized performance).

256 Kbytes external code/data memory
1 Kbyte on-chip data RAM
40 bytes general-purpose registers in the CPU

The programmable counter array of the 8x930Ax USB Controller gives it increased flexibility for applications that require real-time compare/capture, high-speed I/O and pulse-width modulation capabilities.

The controller also includes:

An enhanced serial port
Three 16-bit timer/counters
A hardware watchdog timer
Four 8-bit I/O ports
Two power-saving modes: idle and power-down