Connection Test

The Connection Test tab on the XJRunner Setup screen provides the ability to customise the actions of the connection test. The default settings are intended to be suitable for most projects, but if you are experiencing problems running the connection test these options can be useful in tracking down and fixing the problem. The Reset default settings button allows options to be reset to the initial values if needed.

Output

These settings control the default output level of the connection test when run using the CONNTEST built-in function.

• The Default error detail level sets the level of detail which is displayed when an error is found by running the connection test.
• Selecting the Suppress progress messages option will stop any progress messages from being displayed when the connection test is run.
• Selecting the Reduce output for Test Fixture boards option simplifies connection test error reports by hiding information about nets on boards marked as Test Fixture boards. In the net detail for error reports, nets on Test Fixture boards will appear as single pin nets, showing only the pin on the connector device. In the error detail, all JTAG data for devices on Test Fixture boards will be displayed as if the connector pin were reading/writing those values. This setting can be changed in XJRunner by users who have appropriate privileges.
• The Show link to view all test data checkbox allows will enable the Connection Test Output Viewer, which is accessed by clicking a link in the output when running tests, or by right-clicking on errors found by the Connection Test. The viewer allows the user to see all data from the connection test rather than just the data specific to a particular error.

Maximum Simultaneously Changing Nets

This setting determines the maximum number of nets which can change value simultaneously. It is useful to set this limit if the power supply of the circuit is unable to cope with large numbers of nets changing state at once, leading to ground bounce/voltage problems. The default value of 0 is a special case meaning there is no limit to the number of nets which can change state simultaneously.

Indirect Shorts (shorts via resistor) Testing

The default setting for Connection Test is to test all nets in the circuit for indirect shorts (short circuits on the far side of a resistor from any JTAG device) where possible. In the event that this generates spurious errors (it is possible for floating nets to mimic this situation) then selecting Reduced Sensitivity will limit the indirect-short testing to nets which have Connections defined or which are linked via Passive Devices. This also reduces the sensitivity of the Connection Test fault analysis, to reduce the chances of floating nets appearing to be shorted to each other.

If the Ignore one-way indirect shorts option is unchecked, Connection Test will include diagnosis of one-way indirect shorts (e.g. through a buffer and a resistor). However, the behaviour of a floating net can sometimes mimic this behaviour, causing spurious errors to be reported. The default is to ignore these apparent shorts because of the likelihood of spurious failures, but you can change this to raise sensitivity if you require it.

Shorts to Unconnected Pins

Some JTAG devices have a tendency to pick up noise from the circuit on pins which are not actually connected to any other pin on the board. This may show up as unexpected short-circuit errors. Check the Ignore shorts to unconnected pins checkbox if this a problem in your circuit. Typically this might manifest itself as a yield issue where some boards fail Connection Test but pass when the test is re-run.

Logic Testing Options

Checking the Enable logic testing checkbox will make the Connection Test automatically test connections that pass through logic devices that you have defined in the project. By default, this option is enabled.

Delay between JTAG scans

This option allows a specified number of TCK cycles to be inserted between the Connection Test's JTAG scans, thus allowing relatively small delays to be inserted (given that a scan typically takes several hundred TCK cycles). This can be useful if the circuit contains items such as weak pull resistors or slow logic devices which otherwise cause test failures because they are not fast enough to respond to their inputs.

1149.6 Testing Options

These options only have any effect if there is at least one JTAG device in the circuit which is compatible with the IEEE 1149.6 standard.

The Enable 1149.6 testing option allows the advanced 1149.6 testing to be switched off and on at a circuit level. Turning the 1149.6 testing off will make the connection test take less time but it won't be able to detect as many possible faults on high-speed pins which expect to use this standard.

The Override 1149.6 test time setting allows the user to override the time spent during 1149.6 tests between JTAG scans at a circuit level. If this is not set, device settings and BSDL file parameters will determine this time automatically. This option allows some troubleshooting of strange behaviour in supposedly 1149.6-compliant devices.

Multiboard Performance

The Check for inter-board short circuits option is useful for performance in large circuits with multiple circuit boards (e.g. testing a populated chassis). The checkbox is checked by default. Unchecking it means the Connection Test will assume nets entirely contained within one board cannot be shorted to nets entirely contained in a different board (it is assumed to be physically impossible for them to touch.) This can significantly improve connection test speed in very large systems with multiple circuit boards. Nets which are connected between boards will still be tested for shorts against all of the boards they are connected to.

Differential Signals

The Always drive differentially option forces differential driving in the case where two (non-paired) JTAG output pins are connected to a grouped-port input differential pair, meaning that if one leg of the differential pair is driven, the Connection Test will make every effort to drive the other leg too.

This feature is useful with some devices in which in the silicon manufacturer has made errors in their differential receiver implementation. The setting causes a minor reduction in test coverage on the differentially-paired nets involved and so is not enabled by default.