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Hardware options supporting ScanWorks are many and varied

The many testing and programming capabilities of ScanWorks' software-based tools would be of little use unless they could be connected to the board or system that's being tested. And that's where ASSET's hardware products come in.

For ScanWorks, the test platform is either a standard PC, a CPU-based board or a system with a built-in (embedded) boundary-scan controller. A standard PC can function as a stand-alone bench-top ScanWorks test development station, a repair station, or a manufacturing test station. Or, ScanWorks can be configured as part of an Agilent 3070 in-circuit tester, a Checksum manufacturing defect analysis (MDA) system or a functional test bed in a PXI chassis.

In all cases, physical hardware connects the ScanWorks software to the unit under test (UUT), which may be either a board or a system. There are four categories of ScanWorks hardware: boundary-scan controllers, interface pods, buffer boards, and boundary-scan IO modules. Other hardware accessories include cables that connect ScanWorks hardware to the UUT or to a demonstration board.

PCI and PXI Boundary-Scan Controllers

The primary function of ScanWorks' boundary-scan controllers is to control how test vectors are applied to the UUT. The vectors created by ScanWorks are transferred over an internal PC bus to the boundary-scan controller. The controller accepts data and commands from ScanWorks software and manipulates the IEEE 1149.1 Test Access Port (TAP) signals to accomplish the test or programming activity.

With today’s technology, the PCI bus is the most efficient PC bus for boundary-scan applications. It supports a data throughput rate fast enough to support any test application and it is a very reliable bus. The PXI bus is an extension of the PCI bus and it also is very efficient. Other PC interfaces such as a PC's parallel port or a serial bus can be used but, generally, these are not fast or reliable enough except in special applications. Nevertheless, ScanWorks can be connected to the UUT through a PC's parallel port. In addition, ASSET is developing a USB 2.0 boundary-scan controller.

ScanWorks has three controllers that interface to the PCI or PXI buses:

• PCI Single-Port Boundary-Scan Controller (PCI-100 Hardware Kit)
• PXI Single-Port Boundary-Scan Controller (PXI-100 Hardware Kit) For more information on the PXI-100, click here.
• PCI Multiport Boundary-Scan Controller (PCI-400 Hardware Kit)

Each of these controllers has specific features that are particularly useful for certain applications. Taken as a group, the ScanWorks controllers offer features and capabilities for all of the most widespread applications of boundary scan.

The PCI Single-Port Boundary-Scan Controller (PCI-100) is ScanWorks' workhorse controller. Its throughput is fast enough for most applications and it can be interfaced to most boards being tested. In many cases, it can be used without an interface pod. At the user's discretion, an interface pod is sometimes installed between the ScanWorks controller and the UUT. The interface pods for the PCI-100 and PXI-100 extend the range of voltages supported by the controllers to 1.8V-5.0V and lengthen the allowable distance between the PC and the UUT. For more information, see the section below on interface pods.

The low cost of the PCI-100 controller makes it an attractive choice for manufacturing stations. It supports one set of TAP signals, but the signals can be expanded to four TAPs with the Multitap Buffer Board or the Four-TAP Buffer pod, which are described later in this article. As many as eight PCI Single-Port Boundary-Scan Controllers can be installed in one PC-based test platform.

The PXI Single-Port Boundary-Scan Controller (PXI-100) has the same features as the PCI-100, but it comes in a PXI 3U form factor. It has been designed for functional test environments where PXI has become the dominant technology. The PXI-100 interfaces to the same pods or buffer boards as the PCI-100, making for an easy transition from a bench-top environment in development to a functional test environment in manufacturing. As many as eight PXI Single-Port Boundary-Scan Controllers can be installed in one PXI-based test platform.

Interface Pods for the PCI-100 and PXI-100 Controllers

An interface pod is sometimes installed between the ScanWorks controller and the UUT to extend the range of voltages supported by the controller to 1.8V-5.0V and to lengthen the distance between the controller card and the UUT.

ScanWorks supports two interface pods for the PCI-100 and PXI-100: a Single-TAP Boundary-Scan Interface Pod and a Four-TAP Interface Pod. These interface pods are bundled with the PCI-100 and the PXI-100 controller cards in the PCI-100 and PXI-100 Hardware Kits, or they can be purchased separately.

The Single-TAP Boundary-Scan Interface Pod provides an interface for a configuration where the tester is not in close proximity to the board being tested. With the Single-TAP Interface Pod, the board under test can be up to 15 feet away from the host PC and the maximum test clock frequency still can be maintained. If a reference voltage is provided by the board being tested, the Single-TAP Interface Pod supports automatic voltage selection. The Single-TAP Boundary-Scan Interface Pod comes in a sturdy enclosure for ruggedness.

The Four-TAP Interface Pod supports the same scan path control features as the Multitap Buffer Board (see section below on ScanWorks Buffer Boards). The four TAPs are enabled by switches on the Four-TAP Interface Pod or by discrete IO signals from the PCI-100 or PXI-100 Boundary-Scan Controllers. If more than one secondary TAP is active simultaneously, the active TAPs are connected serially to form one scan chain. The Four-TAP Interface Pod supports a range of voltages from 1.5 to 5.5V, in 0.3V increments. The voltage is selected by on-board switches or by discrete IO signals from the PCI-100 or PXI-100 controllers. TAP signal termination is configured by on-board jumpers. The Four-TAP Interface Pod comes in a sturdy enclosure for ruggedness.

PCI-400 Multiport Boundary Scan Controller

The PCI Multiport Boundary-Scan Controller (PCI-400) is a high throughput, flexible controller designed for a high-volume manufacturing environment. The drivers for the PCI interface to the host PC have been optimized for 30 percent faster throughput than the PCI-100 at the same test clock (TCK) frequency. The PCI Multiport Boundary-Scan Controller requires a Four-Port Boundary-Scan Interface Pod to connect to the UUT. The pod can be up to 50 feet from the controller card and still support the maximum TCK frequency of 50 MHz. The PCI Multiport Boundary-Scan Controller can support two Four-Port Boundary-Scan Interface Pods and as many as three PCI Multiport Boundary-Scan Controllers can be installed in one PC. In a maximum configuration, one test platform can connect to as many as 24 scan paths (2 x 4 x 3 = 24). ScanWorks provides the software to easily manage multiple scan paths.

Because the PCI Multiport Boundary-Scan Controller is embedded in the Agilent ScanWorks for the 3070 in-circuit test system, the transition from development to 3070 ICT systems in manufacturing is quite seamless.

Interface Pod for the PCI-400 Controller

The Multiport Boundary-Scan Controller (PCI-400) requires the use of one or two Four-Port Boundary-Scan Interface Pods. The pod has four test ports, each of which supports the IEEE 1149.1 TAP signals and four discrete IO signals for special applications. This pod supports a TCK frequency up to 50 MHz. The interface to a board being tested can be easily optimized with software-configurable impedance matching circuits. ScanWorks software remembers the settings for each board type and automatically configures the Four-Port Boundary-Scan Interface Pod when the ScanWorks project for that board is loaded.

Controllers for ScanWorks

ScanWorks Buffer Boards

The primary function of a buffer board is to provide a reliable interface for ScanWorks to the board or system being tested. Board designers often do not make boundary-scan one of the primary considerations during design and layout. As a result, the interface provided for the IEEE 1149.1 TAP signals sometimes is not implemented well. Signals may not be properly buffered or terminated, or the TCK and TMS signals may be distributed to too many devices. Furthermore, the interface to the TAP signals might consist of several scan paths when a single scan path would provide more efficient operation. Installing one of ScanWorks' buffer boards close to the UUT can alleviate many of these problems.

ScanWorks has two buffer boards available: a Single-TAP Buffer Board and a Multitap Buffer Board. Buffer boards can be used with any of the ScanWorks controllers or interface pods.

The Single-TAP Buffer Board provides an ACQ244 buffer with accessible termination resistors so they can be changed to match the impedance of the board being tested. Once the proper configuration is determined, the buffer board can be built into the UUT's test fixture. The ACQ244 supports a range of logic levels from 2.5V to 5.0V. The voltage provided to the Single-TAP Buffer board should be matched to the UUT logic level to be supported.

The Multitap Buffer Board provides the same buffering as the Single-TAP Buffer Board, but it supports four sets of TAP signals. The four secondary TAPs are enabled by switches on the Multitap Buffer Board or by discrete IO signals from the PCI-100 or PXI-100 boundary-scan controllers. If more than one secondary TAP is active, the active TAPs are connected serially to form one scan chain. In this way, the length of the scan path can be optimized for fast access or multiple scan paths can be combined to improve test coverage between devices on separate scan paths. Usually, buffer boards eventually are designed into the test fixture for the board being tested.

Boundary-Scan IO Module

The primary function of ScanWorks' boundary-scan IO modules is to provide test access to off-board signals that otherwise could not be accessed by a boundary-scan test system. For many designs, boundary scan has adequate access to on-board signals, but signals that go off the board often can not be tested by boundary scan. By adding boundary-scan access to these off-board signals, a ScanWorks boundary-scan IO module can increase the board's test coverage with boundary scan, possibly reducing the need for implementing another test method or for developing alternative tests to reach the required level of test coverage.

The Boundary Scan 400 IO module (BSIO-400) provides 400 boundary-scan accessible test channels that can be used to control and observe signals that go off the board. Each channel is controlled individually and can be configured as an input or output. The BSIO-400 scan path can be combined with the scan path of the board being tested so it is included in scan path verification and interconnect tests. Eventually, the BSIO-400 should be designed into the UUT test fixture.

Cables

The standard cables needed to connect boundary-scan controllers, pods and buffer boards to a UUT come as part of the various ScanWorks hardware kits or they can be acquired individually as replacements or spares.

Because there is no standard connector type or pin-out for IEEE 1149.1 TAP connectors, many different types of cables are used by board designers. And since ASSET can not possibly stock cables for all applications, the cables that ASSET provides conform to the ScanWorks standard pin-outs. The TAP signal cables that come with PCI-100 and PXI-100 conform to a ScanWorks standard 14-pin header pin-out, while the cables for the PCI-400 have a ScanWorks standard 20-pin header format to accommodate the discrete IO signals that accompany each PCI-400 test port. An adapter is provided with the PCI-400 Kit to convert the 20-pin header pin-out to the 14-pin header pin-out if the discrete IO signals are not used. For other applications, the user must adapt the cables to the specific UUT.

There are two options for adapting ScanWorks cables to a UUT:

1. Remove the cable connector that came with ScanWorks and replace it with the appropriate connector for the UUT. This provides the least impedance mismatch, and is recommended for applications that require the fastest TCK possible.
2. For systems where high throughput is not required and a lower TCK frequency can be tolerated, an adapter cable can be used. This adapter cable should be as short as possible and a careful analysis of its signal integrity should be done.

Demonstration Board

ASSET's ScanLite demonstration board is used for training purposes or as a known-good UUT when troubleshooting a problem with the interface to a UUT. ScanLite demonstrates the primary test applications of ScanWorks, including scan path verification, interconnect testing, memory access verification, cluster testing, PLD programming and flash memory programming. Complete design information such as schematics and layout data, as well as a completed ScanWorks project are provided with ScanLite.

Conclusion

ScanWorks' variety of hardware options gives users a high degree of flexibility for interfacing UUTs to ScanWorks, ensuring that the needs of most applications will be met effectively. For special requirements, please contact an ASSET application engineers to discuss the application.