Termination and Protection Board

The Termination and Protection Board is designed to improve operation when using an XJLink2 in a situation where the Unit Under Test (UUT) has unterminated JTAG signals. It typically improves signal integrity, often meaning the JTAG chains can operate at a higher speed, and also provides some transient protection to both the UUT and the attached XJLink2, which can prevent damage to either unit during power-up or while connecting/disconnecting equipment.

The board operates simply, by introducing a 50 Ω resistor between each of the 18 IO pins on the XJLink2 connector, and its connection to the UUT. These resistors act as series termination but also provide a limit on voltage/current in the connection.

The board also provides spare pads for each IO that can be used to divide signals in either direction allowing even more flexibility of voltage domains into the XJLink2 as well as extending its effective ADC range.

Note that the resistance on these boards could add a time delay to nets that have significant capacitance – you may need to adjust your project slightly, for example to give reset lines more time to rise/fall.

• Schematic diagram