XJTAG 4.2 introduces three new values that can be set for either Constant Pins or XJEase device file Disable Values.

It also renames the long-standing value “Input” to now be called “Excluded”.

“Excluded” value replaces “Input” in Constant Pins and Disable Values

Changing constant ‘Input’ pins to be called ‘Excluded’ is simply a name change to improve clarity for people learning to use XJTAG, and does not affect project compatibility. Existing projects will not be affected except that constant ‘Input’ pins will show as ‘Excluded’ in the relevant sections in XJDeveloper 4.2.

In XJAnalyser the same value is still called ‘Input’ because it makes more sense in that context, and translation between the two is automatic.

Also, in XJEase device files that use XJEaseDoc entries to set up configuration defaults, if the file uses the @defaultvalue tag, XJEase will accept a value of either ‘excluded’ or ‘input’.

New Constant/Disable Pin Values

Constant Pins and Disable Values traditionally have had three possible values: High, Low and Excluded (previously called ‘Input’). High and Low instructed XJTAG to drive the net to those values if possible. From version 4.2 there are three new values that can be set: IsHigh, IsLow, or IsDriven. All of these new values (along with the existing ‘Excluded’ value) tell XJTAG that it should not drive the net. The new values exist to state that something outside of XJTAG’s control is driving and/or that we expect a certain value to always be present on the net. If the net can be read then Connection Test will read it to verify that nets with a constant value of IsHigh or IsLow are always read at their expected value, and a connection test error will be reported if the net is read at the opposite value at any point during the connection test.

The value Excluded (previously ‘Input’) tells the connection test not only to avoid driving the net, but also to ignore all values read from the net. The new value IsDriven allows Connection Test to read the net in order to diagnose short-circuit errors without driving the net, and is intended for nets which are known to be driven by something outside XJTAG’s control but which are not expected to hold a constant value. If you set a value of IsDriven but see spurious errors on a net, then setting the value to Excluded will solve the issue, with a minor loss of test coverage.

Using the new values as Disable Values for busses in a Test Device file will imply strongly to the reader of the project that the test device is the device that is driving the net. If this is not the case then using a Constant Pin is probably more appropriate.