Boundary-scan is an integrated method for testing interconnects on printed circuit boards PCBs that are implemented at the integrated circuit IC level. Since its introduction as an industry standard inboundary-scan also known as JTAG has enjoyed growing popularity for board level manufacturing test applications.

Boundary-scan has rapidly become the technology of choice for building reliable high technology electronic products with a high degree of testability. Due to the low-cost and IC level access capabilities of boundary-scan, its use has expanded beyond traditional board test applications into product design and service. This article provides a brief overview of the boundary-scan architecture and the new technology trends that make using boundary-scan essential for dramatically reducing development and production costs, speeding test development through automation, and improving product quality because of increased fault coverage.

The article also describes the various uses of boundary-scan and the tools available today for supporting boundary-scan technology. The inability to test highly complex and dense printed circuit boards using traditional in-circuit testers and bed of nail fixtures was already evident in the mid eighties.

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Due to physical space constraints and loss of physical access to fine pitch components and BGA devices, fixturing cost increased dramatically while fixture reliability decreased at the same time.

Since that time, this standard has been adopted by major electronics companies all over the world. Applications are found in high volume, high-end consumer products, telecommunication products, defense systems, computers, peripherals, and avionics.

In fact, due to its economic advantages, some smaller companies that cannot afford expensive in-circuit testers are using boundary-scan. The boundary-scan test architecture provides a means to test interconnects between integrated circuits on a board without using physical test probes.

JTAG Architecture

It adds a boundary-scan cell that includes a multiplexer and latches to each pin on the device. Boundary-scan cells in a device can capture data from pin or core logic signals, or force data onto pins. Captured data is serially shifted out and externally compared to the expected results. Forced test data is serially shifted into the boundary-scan cells. All of this is controlled from a serial data path called the scan path or scan chain. Figure 1 depicts the main elements of a boundary-scan cell.

By allowing direct access to nets, boundary-scan eliminates the need for a large number of test vectors, which are normally needed to properly initialize sequential logic. Tens or hundreds of vectors may do the job that had previously required thousands of vectors.User Data Register s. Before discussing about the Boundary Scan Register, it is important to understand why we need it.

Consider a case where we have 3 chips from different vendors and we want to assemble it on one board. But when we put them together on a board, there are chances of faults in the interconnections between the chips, then how are we going to detect that?

We cannot take our board to the ATE and test all the chips again only for the purpose of testing the interconnections ATE is highly expensive. The Boundary Scan Registers solves these problems.

jtag in vlsi

The JTAG interface allows for several devices to be connected to a single interface in a daisy chain configuration. It allows devices in a circuit to be tested with minimal timing overhead. Suppose we have multiple chips connected in series as shown in Figure 4 and we want to access a particular chip, say Chip To avoid this delay we have bypass register which introduces only 1 clock delay per JTAG device.

To bypass a Chip, we load the opcode value of the Bypass Register in the Instruction Register for the Instruction Decoder to establish a path through the Bypass Register.

It is only required for Device identification. The Device ID Code value enables a user or debugger tool to identify the debug port to which it is connected. You can refer the example shown here to understand how we can control an internal logic using the User Data Register.

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The Hold Register stores the previous data and the Shift Register is used to shift-in the next data without affecting the stored data. It is important to note that, we can have multiple User Data Registers, with each register having a unique opcode. Skip to content. Figure 1: An example showing 3 chips assembled on a board and its interconnections.

Figure 4: An example showing how Bypass Register is used. Figure 6: A top level view of User Data Register. Share this: Twitter Facebook. Like this: Like Loading Post to Cancel. Control signals. Shift DR. Functional Mode thus BSC is transparent. Load shifted data from flop-1 to flop Load data from Data Input to flopThis document provides you with interesting background information about the technology that underpins XJTAG. Advances in silicon design such as increasing device density and, more recently, BGA packaging have reduced the efficacy of traditional testing methods.

This standard has retained its link to the group and is commonly known by the acronym JTAG. The main advantage offered by utilising boundary scan technology is the ability to set and read the values on pins without direct physical access. The process of boundary scan can be most easily understood with reference to the schematic diagram shown in figure 1. In normal operation these boundary scan cells are invisible.

Not all boundary scan cells are the same — there are 10 types of cell in the There are two types of registers associated with boundary scan. Each compliant device has one instruction register and two or more data registers.

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Instruction Register — the instruction register holds the current instruction. Its content is used by the TAP controller to decide what to do with signals that are received. Most commonly, the content of the instruction register will define to which of the data registers signals should be passed. Other data registers may be present, but they are not required as part of the JTAG standard. Figure 2, below, shows the state-transition diagram.

The two main paths allow for setting or retrieving information from either a data register or the instruction register of the device. The data register operated on e.

The IEEE These instructions are:.

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Introduction Advances in silicon design such as increasing device density and, more recently, BGA packaging have reduced the efficacy of traditional testing methods. Boundary Scan The main advantage offered by utilising boundary scan technology is the ability to set and read the values on pins without direct physical access. Figure 1 — Schematic Diagram of a JTAG enabled device The process of boundary scan can be most easily understood with reference to the schematic diagram shown in figure 1.

TCK Test Clock — this signal synchronizes the internal state machine operations. It is sampled at the rising edge of TCK when the internal state machine is in the correct state. Registers There are two types of registers associated with boundary scan.

BSR — this is the main testing data register. It allows other devices in a circuit to be tested with minimal overhead. The file contains details of the Boundary Scan configuration for the device. For more detail on each state, refer to the IEEE This instruction allows the testing of other devices in the JTAG chain without any unnecessary overhead. However, the device is left in its normal functional mode.

During this instruction, the BSR can be accessed by a data scan operation to take a sample of the functional data entering and leaving the device. Obtaining the IEEE And how can I make use of it? Testing BGA Connections. This site tracks visits anonymously using cookies.Post a Comment. What is MCMM?

It can also have annotation data, such as SDF or parasitics files. Many chip have multiple modes such as functional modes, test mode, sleep mode, and etc. What's a Corner A corner is defined as a set of libraries characterized for process, voltage, and temperature variations. Corners are not dependent on functional settings; they are meant to capture variations in the manufacturing process, along with expected variations in the voltage and temperature of the environment in which the chip will operate.

There are a total of thirty six possible scenarios at which all timing checks, such as setup, hold, slew, and clock gating checks can be performed. Running STA for all thirty six scenarios at the same time can be prohibitive in terms of runtime depending upon the size of the design. It is possible that a scenario may not be necessary as it may be included within another scenario, or a scenario may not be required.

Design for Test (DFT) Guidelines

For example, the designer may determine. Labels: sta. No comments:. Newer Post Older Post Home. Subscribe to: Post Comments Atom.Want to improve the overall test coverage of your assembled boards? Signals can be driven via boundary-scan and sensed with the flying probes or the other way around.

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Results and diagnostics are presented in the Takaya software environment. For the flying probe tester integration, a standard JT pod is used. Results and diagnostics are presented in the Leonardo run-time GUI. Both solutions are controlled by the Teradyne GUI and reports with full pin level diagnostics are fed back into the Teradyne report generator. Our ProVision development tools can be used to generate the boundary-scan based test patterns which are provided to the Teradyne test development tools for further processing.

ProVision also controls the placement of the probe.

Designing for Boundary Scan, JTAG, Test

Combining the analog signature analysis I-V trace capability of the Huntron system with boundary-scan creates an excellent mixed signal tester platform.

JTAG Technologies has a long-standing partnership with Seica Spa, Italy with whom we developed one of the earliest flying-probe and boundary-scan test integrations. Together with the engineers of Viavi Solutions we developed an Viavi dedicated version of our QuadPod that fits perfectly in to a 42xx tester. In addition an enhanced version of our execution software has been developed that interacts with the pin cards of the Viavi and its GUI. Results and diagnostics are presented in the Viavi environment.

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For more information visit the Viavi website. We have been able to solve thousands of board test problems by actively engaging with our customers. Once you become a JTAG Technologies customer you are an integral part of our business with free access to our world-wide support network.

ATE integration. ATE Integration Want to improve the overall test coverage of your assembled boards? Read more.

DFT Training

Download datasheet. Keysight was Agilent. Viavi Solutions was Aeroflex. Happy to serve you! Contact FAQ.To better address problems of board-level testing, several design for testability standards have been developed.

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The primary goal of these proposed standards is to ensure that chips of VLSI complexity contain a common denominator of DFT circuitry that will make the test development and testing of boards containing these chips significantly more effective and less costly.

The description of a board-level test bus presented on IEEE Figure below shows a general form of a chip which supports IEEE The application logic represents the normal chip design prior to the inclusion of logic required to support IEEE The test-bus circuitry, also referred to as the bus slave consists of the boundary-scan registers, a 1-bit bypass register, an instruction register, several miscellaneous registers, and the TAP.

Test instructions and test data are sent to a chip over the TDI line. Test results and status information are sent from a chip over the TDO line serially. The sequence of operations are controlled by a bus master, which can be either ATE or a component that interfaces to a higher-level test bus Control of the test-bus circuitry is primarily carried out by the TAP, which responds to the state transitions on the TMS line.These guidelines should not be taken as a set of rules. The potential advantages in terms of testability should be considered together with all other implications which they may have e.

It is assumed that readers of this document have a minimal familiarity with the IEEE standards The more JTAG devices that are incorporated into a circuit the greater the number of nodes that can be fully exercised and tested. The In order to use this functionality it is important to ensure that nets to be tested in this way have Compliance with the It is important that nTRST signals are not connected directly to ground as this would completely disable JTAG, not only for an individual device but for the complete scan chain.

If possible, route the TAP signals away from other active signals to reduce noise and improve signal integrity. The serial JTAG interface will typically run with a clock rate of 10 MHz to 30 MHz, and poor layout can induce errors that are very difficult to pinpoint and can require a board re-spin to fix. It may be necessary to have some devices directly connected to their own connectors for debug purposes during development or programming. Adding the option to link these connectors into a single chain for manufacturing test maybe beneficial and reduce both BOM Bill of Materials and handling costs during production.

Interleaving active signals with ground connections will minimize these effects. If the number of pins available on the connector makes this impractical then prioritise placing TCK next to ground.

It is very important to have a strong ground connection between the JTAG controller and the board under test. If there are any spare pins on the JTAG connector to the board then adding extra ground signals will be beneficial.

The XJLink2 has fixed ground connections on pins 10 and 20 so connecting these will improve signal integrity. Ideally each new design will use the same connector type and signal layout so cables can be reused.

jtag in vlsi

Routing the TAP signals to spare pins on other connectors may enable access to the scan chain even if the dedicated test access connector is unfitted or inaccessible. On some devices TAP pins can be configured to have functions other than The function of these pins is normally configured by sampling other pins on the device as it is reset.

Depending on the requirement of the design this configuration can be achieved in several ways:. Many synchronous devices can be tested by boundary scan however this will be dependant on the source of the clock.

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