PRODUCT HOW-TO: Using the Blackfin Processor for Bus-Powered USB 2.0 Compliant Designs

Developers can connect a PC via USB to the ICE-100B, which plugs into the design's Joint Test Action Group (JTAG) interface. In previous versions, USB data connectivity to the emulator was available, but it required separate power. The latest version lowered cost and product size by moving to USB bus-power.

Figure 2: ICE-100B, USB 2.0 bus-powered Blackfin emulator

The JTAG interface of ADSP-BF52x processors can be operated at 1.8 V, 2.5 V, or 3.3 V in a custom application. Thus, one requirement of the new ICE-100B was to be compliant with any of the three operating voltages. This allows the same emulator to be used on boards with different target voltages.

Because the ADSP-BF527 VDDEXT power domain has the flexibility to natively operate at any of these voltages, the ICE-100B target voltage is configurable via a jumper.

Testing results of the ICE-100B showed current consumption of 77.6 mA unconfigured and 92 mA when configured. Current consumption in response to the USB sleep command is an amazingly low 352 A. The emulator signals high-speed attachment (PHY pulls D+ signal high) to the host 60 ms after VBUS reaches 4.1 V.

A Note Regarding Preliminary USB Testing
USB products utilizing Blackfin processors must meet USB specifications to be added to the USB-IF integrators list. A good portion of the USB certification testing can be performed with just an ammeter, an oscilloscope, and a PC. Testing as much as possible in house before utilizing a contract test laboratory can mean great savings.

The USB.org website provides links to download the "USB 2.0 Command Verifier" (CV) and the "High Speed Electrical Test Toolkit" (HSET). CV allows testing of USB Chapter 9 tests, which include device descriptors, hibernation, and enumeration. HSET can be used to enter USB standard test modes and to measure the unconfigured and configured current consumption.

The Big Picture
The ADSP-BF527 processor offers significant performance, low cost, and a small package. Combining this processor with other ADI products (USB software stack, power regulators, reset supervisors, and the latest generation of low-cost emulators) provides users with a comprehensive set of building blocks to design USB products.

References
1) ADSP-BF52x datasheet
2) ADSP-BF52x Blackfin Processor Hardware Reference (Volume 1 of 2)
3) ADSP-BF52x Blackfin Processor Hardware Reference (Volume 2 of 2)
4) Universal Serial Bus Specification
5) ADM6384 datasheet
6) ADP170 datasheet
7) ADP121 datasheet

Gregory Coppenrath [gregory.coppenrath@analog.com] has been a hardware engineer in ADI's DSP tools group at Analog Devices, Inc. since 2006. He received a BSEE from Worcester Polytechnic Institute (WPI) in Worcester, MA in 2001, and an MSEE from the University of Massachusetts, Lowell in 2005. Prior to working at ADI, Greg worked at MRV Communications designing console servers for remote access.