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Issue #213 April 2008
Programmable Power
Build a Simple USB DAC
by Yoshiyasu Takefuji
Start | USB Communications | Firmware | MAX517 (DAC) Programming | Firmware, Software, & LIBUSB | Host Device Driver Installation | Testing | Sources & PDF
USB COMMUNICATIONS
USB 2.0 has three communication types: 1.5 Mbps (low speed), 12 Mbps (full speed), and 480 Mbps (high speed). I established 1.5-Mbps low-speed communication using an ATtiny45 with a 12-MHz ceramic resonator without a USB chip.
An open-source software protocol stack can take care of non-return-to-zero inverted (NRZI) encoding, decoding, and bit stuffing for synchronization. The conventional USB chip uses NRZI encoding/decoding with automated bit stuffing. In the bit-stuffing technique, each time a series of five consecutive “0” bits is transmitted, a “1” bit is automatically added to force a transition. In this article, usb_control_msg and usbFunctionSetup functions are used for USB communications. usb_control_msg is used for host PC USB communications. usbFunctionSetup is used for ATtiny45 USB communications.
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