Constant Pins

Like Bus Disable Values, Constant Pins allow you to define pins which XJTAG will keep in a constant state during automated testing such as the Connection Test.

A Constant pin is observed during automated testing but will be overridden during XJEase testing if a bus value is set which conflicts with the constant value.

A constant pin can have one of 6 values: High, Low, IsHigh, IsLow, IsDriven or Excluded.

Constant values of High or Low instruct XJTAG to drive the value to the net during the Connection Test and in the initial scan of the chain, if it can.

The other constant values tell XJTAG not to drive the net if possible. Values of IsHigh or IsLow inform XJTAG that it can assume the specified value is driven to the net by something that is not JTAG-controlled. IsDriven informs XJTAG that something else is driving the net but that it can still analyse the net for errors. Finally, a value of Excluded means that Connection Test will not drive the net containing this pin, and nor will it analyse the behaviour of this net if it can be read during the test.

In versions of XJTAG prior to 4.2.0, the Excluded value was called Input. The behaviour has not changed and older projects will still work correctly.

Constant pins are set up using the Constant Pins Screen in XJDeveloper.

Constant Pins in XJAnalyser

XJAnalyser still uses the value Input instead of Excluded because in XJAnalyser the value tells the system to initialise the pin to a non-driving state in which it can be read.

In XJAnalyser there are only 3 values of constant pin that can be set - High, Low and Input. When using XJAnalyser to open an XJDeveloper project, existing constant pins will be observed and can be viewed, but the values IsHigh, IsLow and IsDriven are functionally equivalent to Input/Excluded and XJAnalyser will not complain if, for example, an IsHigh pin is read as low.