What is Boundary Scan Test?
Boundary Scan Testing was created to test printed circuit boards for interconnect errors such as: shorts, opens and stuck-at faults that are typically caused by problems in the manufacturing process. Boundary Scan can also be used to functionally test devices such as: RAM, FLASH, I/O and Logic.
How Does Boundary Scan Testing Work?
Boundary Scan uses a method know as “pins-out” testing. Pins-Out testing is implemented on an IC that supports Boundary Scan by including a test cell on each of the IC’s pins.
These cells contain test logic that can control signals into and out of each of the IC’s external pins. Using this technique, signals can be sent between chips that have connected pins (or nets). The diagram to the left below shows how two such devices can be used in a test for shorts circuit failures.
To allow control of the on-board Boundary Scan cells, each device has a serial bus comprised of at lease four standard signals: TDI, TDO, TMS and TCK. An external Boundary Scan tester can be connected to these pins and control the tests being sent to the board via host based software.
Functional Test with Boundary SCAN
Boundary Scan can also test non-Boundary SCAN devices that are connected to at least one Boundary Scan Device. As shown in the diagram to the right, the Boundary Scan test cells at each pin can place signals onto the address, data and control lines of the non-Boundary-SCAN device.
As an example, if this were a RAM device the lines could be manipulated to produce single-beat read and write cycles to the device. This technique can even be used to test I2C and SPI based devices.
What Kinds of Products are Available for Boundary Scan Testing?
There are several types of products available to do Boundary Scan testing (also known as JTAG Controllers). The main types are:
- USB Cable to Boundary Scan controller
- PCI Card to Boundary Scan controller
- Network Interface to Boundary Scan controller
All three system simply connect a host computer that is used to create and run tests to the Boundary Scan interface hardware that controls the device under test. The host software can run the gamut from simple pin wiggling applications to full blown test development.