JTAG

You probably already used tools with jtag interfaces. In fact, processors usually make use of jtag to access debugging and emulation functions. However, jtag is much more than a debugging tool. That is only one aspect of the underlying four-wire jtag communication protocol which can be used for many other purposes. For more information, contact Pertech Embedded solutions.

Important information about jtag

The signals, known as TAP, are part of the IEEE Std. 1149.1. This technology enables testing of Printed circuit board assemblies (PCBA’s) without requiring the same level of physical access needed to perform bed-of-nails testing, or the custom development required to perform a functional test. TAP was specifically designed to interface with devices implanted with new registers implemented for this testing method.

However, the benefits of the TAP register access for debugging and programming were soon recognized. The primary jtag testing dedicated register added to a given device is the boundary scan register (BSR)- named for the position of the individual cells of the register in the device boundary, between the functional core and the pins connecting it to the board. Hence the common parlance to jtag testing as a “boundary scan”.

What started out as just another testing method, became significantly important. Why? Because more and more devices are supplied in BGA (Ball Grid Array) packaging, which imposes rather strict limitations on how testing can be performed with the traditional bed of nails or flying probe techniques.

In contrast, the jtag scan allows control and monitoring of signals on the enabled devices without any need for direct physical access.We should also note that jtag also has two major added benefits: time and money.

Contact the jtag professionals

Flying probe tests are relatively unexpensive compared to the bed of nails technique – but only at the cost of much lengthier test times. Jtag provides rapid tests with no need for costly fixtures, allowing you to enjoy the best of all worlds. Contact Pertech Embedded solutions today, to learn more and see if this solution is right for your needs.

More information

jtag debugger

What is jtag debugger? Mainly, this process includes four pin components as well as an optional fifth, including test clock, test mode select and test reset. Either way, if you are interested in learning more about this process, contact Pertech Embedded solutions.

The process of jtag debugger – several components

TCK: Test Clock This is the drumbeat, the metronome that determines the pace of the TAP controller. Voltage on this pin simply pulses up and down in a cyclical, steady beat. For every “tick” of this clock, the TAP controller undertakes a single action. Mind you, the JTAG standard does NOT define the speed of this rhythm. The external device controlling JTAG determines the TAP controller speed.

TMS: Test Mode Select The action JTAG undertakes is controlled by Voltages on the Mode Select pin control. You tell JTAG what to do by manipulating the voltage on this pin.

TDI: Test Data-In Data is fed into the chip through this pin. Once again, nothing in the JTAG standard defines this pin's communication protocols. That is totally up to the manufacturer. As far as JTAG is concerned, this pin is simply an ingress method for 1s and 0s to get into the chip. What the chip does with them is irrelevant to JTAG.

TDO: Test Data-Out The data coming out of the chip goes through this pin. communication protocols for this pin, just as for the input pin are not defined by JTAG.

TRST: Test Reset (Optional) This is an optional signal used to reset JTAG to a known good state.

jtag debugging

What the jtag interface does is give manufacturers a tool; a device that enables them to test the soundness of physical connections between pins on a chip. What this means in the context of jtag debugging is that when electrical engineers talk about using jtag to "debug" a chip, they are not talking about software debugging as programmers understand the term. What they are referring to is making sure pin 1 on chip 1 is properly physically connected to pin 2 on chip 2, and that all those pins are functioning correctly. To learn more, contact Pertech Embedded solutions.

Not just jtag debugging

From jtag debugging to so much more, the experts of Pertech Embedded solutions will successfully assist you.

Boundary scan

The boundary scan is a method, which relies on standardized 4 pin structure of the JTAG interface that is used in an increasing number of IC chips. The functions of this interface include:

microprocessors and microcontrollers debugging and rapid testing of connections with external devices lacking embedded software.
logic testing of connections between devices lacking external probes;
Flash memories programming

Almost all modern Printed Circuit Board Assemblies (PCBA’s) contain JTAG/boundary-scan infrastructure. Frequently, these devices are seried into scan chains. Activation of the logic and testing completion is provided externally by a JTAG/boundary-scan controller. Equipment requirements are minimized via JTAG/boundary-scan logic, not just in service but also in manufacturing and design, as the need for performing physical probes and putting in the space and infrastructure required to make it possible. To learn more about this subject, contact Pertech Embedded solutions.

Boundary scan: how is this method different than other testing modes?

First, you are not dependent on expensive test equipment. Instead, you rely on logic and minimal testing tools, making for lower cost and greater effectiveness. Furthermore, this approach requires little physical access – so long as the circuit is designed according to the JTAG standard, it will be susceptible to comprehensive testing.

This approach, originally developed way back in the 1980s for the specific function of the Intel 80486 microprocessor, has become a standard technique used by manufacturers and professionals everywhere to program, debug and test nearly every embedded device that is in use. In fact, most semiconductor manufacturers add the logic required to verify chip functionality into the IC itself. This makes it much easier to perform quality control on complex integrated circuits without recourse to physical test probes.

Accordingly, JTAG/BS is no longer an option – it is a necessity. The reason is simple – the PCB market is transitioning towards higher component density, more complex components and more functionalities. To achieve these functionalities ball grid arrays (BGA), surface mounted technology (SMT), systems in package (SIP), multi-chip modules (MCMs) increased IC pin-count and other technologies making physical access and testing of circuits during operation to be increasingly difficult – for almost any method except for the JTAG / Boundary Scan method.

Contacting the experts

We, at Pertech Embedded solutions, will gladly assist you in every step of the way – as well s answer every question.

Previous slide

Next slide