IEEE JTAG standards

There are a number of IEEE standards which apply to boundary scan testing (JTAG).

Currently Used Standards

1149.1

The original IEEE 1149.1 standard has been updated a number of times between its original ratification in 1990 and the current 2013 version. This standard specifies the core functionality provided by silicon to support boundary scan testing, and the communication protocol by which XJTAG can exchange data with the devices on a PCB. Most devices currently on the market implement the 2001 version or earlier of the 1149.1 standard.

In addition to revisions of the main 1149.1 standard, there are other standards in the 1149.x family. These depend on the functionality and communication protocols described by 1149.1 but add further functionality for specific purposes.

1149.6

The next-most widely adopted boundary scan standard is IEEE 1149.6, which is implemented in a large and growing number of devices. It has better support for testing high-speed devices and differential signalling, including circuits with series-connected coupling capacitors, which act as an open circuit at low frequencies and thus prevent 1149.1 being able to transmit signals.

The 1149.6 standard is supported by XJTAG, however the operation of devices in 1149.6 mode does not translate meaningfully into the XJEase language itself, and so support is provided via automatic test pattern generation within the Connection Test.

For a given JTAG device, the BSDL file specifies which standard the device supports, and XJTAG will automatically generate the appropriate Connection Test for the mix of devices in your circuit. In general, XJTAG can work out everything it needs from the netlist, BSDL files, and classification of devices (e.g. as PDD files representing coupling capacitors). However there are some parameters which can be set on the JTAG Device in XJDeveloper which allow the user to specify certain aspects of the test, and the user can disable 1149.6 testing entirely in the Connection Test settings and revert to a 1149.1 test if they require this.

1149.7

The IEEE 1149.7 standard introduces significant additions and revisions to the protocols used by JTAG to transfer data, and improves the handling of multi-core and SoC devices. However, take-up of this standard is currently very low and patchy. It is still unclear which parts of this standard will become popular; XJTAG is monitoring the situation and is committed to adding support where it is found to be needed.

Other JTAG standards

1149.4

The IEEE 1149.4 standard has existed in multiple revisions for over twenty years, and describes a way for silicon to incorporate some analogue testing capabilities within the JTAG standards. However, we see no real-world take-up of this standard, and no sign that there will be any. XJTAG therefore has no support for the features of 1149.4 and is not expecting this to change.