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2 JTAG Hardware Dongles

Defined: dongle: A small device that plugins into a computer and serves as an adapter .... [snip]

In the OpenOCD case, this generally refers to a small adapater one attaches to your computer via USB or the Parallel Printer Port. The execption being the Zylin ZY1000 which is a small box you attach via an ethernet cable. The Zylin ZY1000 has the advantage that it does not require any drivers to be installed on the developer PC. It also has a built in web interface. It supports RTCK/RCLK or adaptive clocking and has a built in relay to power cycle targets remotely.

2.1 Choosing a Dongle

There are several things you should keep in mind when choosing a dongle.

  1. Voltage What voltage is your target - 1.8, 2.8, 3.3, or 5V? Does your dongle support it? You might need a level converter.
  2. Pinout What pinout does your target board use? Does your dongle support it? You may be able to use jumper wires, or an "octopus" connector, to convert pinouts.
  3. Connection Does your computer have the USB, printer, or Ethernet port needed?
  4. RTCK Do you require RTCK? Also known as “adaptive clocking”

2.2 Stand alone Systems

ZY1000 See: http://www.zylin.com/zy1000.html Technically, not a dongle, but a standalone box. The ZY1000 has the advantage that it does not require any drivers installed on the developer PC. It also has a built in web interface. It supports RTCK/RCLK or adaptive clocking and has a built in relay to power cycle targets remotely.

2.3 USB FT2232 Based

There are many USB JTAG dongles on the market, many of them are based on a chip from “Future Technology Devices International” (FTDI) known as the FTDI FT2232; this is a USB full speed (12 Mbps) chip. See: http://www.ftdichip.com for more information. In summer 2009, USB high speed (480 Mbps) versions of these FTDI chips are starting to become available in JTAG adapters.

2.4 USB-JTAG / Altera USB-Blaster compatibles

These devices also show up as FTDI devices, but are not protocol-compatible with the FT2232 devices. They are, however, protocol-compatible among themselves. USB-JTAG devices typically consist of a FT245 followed by a CPLD that understands a particular protocol, or emulate this protocol using some other hardware.

They may appear under different USB VID/PID depending on the particular product. The driver can be configured to search for any VID/PID pair (see the section on driver commands).

2.5 USB JLINK based

There are several OEM versions of the Segger JLINK adapter. It is an example of a micro controller based JTAG adapter, it uses an AT91SAM764 internally.

2.6 USB RLINK based

Raisonance has an adapter called RLink. It exists in a stripped-down form on the STM32 Primer, permanently attached to the JTAG lines. It also exists on the STM32 Primer2, but that is wired for SWD and not JTAG, thus not supported.

2.7 USB Other

2.8 IBM PC Parallel Printer Port Based

The two well known “JTAG Parallel Ports” cables are the Xilnx DLC5 and the MacGraigor Wiggler. There are many clones and variations of these on the market.

Note that parallel ports are becoming much less common, so if you have the choice you should probably avoid these adapters in favor of USB-based ones.

2.9 Other...