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The applications, debugging, testing, in-system programming of programmable logic (FPGAs and (c)PlDs) or flash memories, etc. are determined by the software being used. For basic testing buzzing-out connections interactively and interactive verification of a cluster (ie a non-boundary scan device surrounded by boundary-scan devices) may already be sufficient. More functionality and automation, eg automatically generate various JTAG boundary-scan applications, run a sequence of test and in-system programing actions, etc. can simply be added by further software modules. A simple controller plus some interactive test capabilities in addition to your normal functional test set-up may be sufficient for debugging and testing prototypes as well as small production series. The JTAG controller plus test and in-system programming software can be used stand-alone, or be integrated with your functional test set-up.: “JTAG Technologies inside”. You can thus scale your JTAG test and in-system programming solution from a simple controller with some basic test software all the way to a fully equipped system with automatic application generators and advanced sequencing capabilities. This makes JTAG a cost-effective approach not only for higher volume production, but also for prototype testing and small volume production. Even if only one device on the printed circuit board assembly (PCBA) has boundary-scan JTAG testing can already be used. The more JTAG access is available on a board the higher the fault coverage via JTAG. The amount of JTAG access on a board not only depends on the number of boundary-scan devices that is present, but also which device types have boundary-scan. If in a CPU-centric or FPGA-centric design only the CPU or the FPGA has boundary-scan and/or a JTAG debug register the fault coverage via JTAG can already be very high. Covering analog and digital Boards contain a mix of analog and digital circuitry. JTAG boundary-scan is mostly limited to digital signals (although an analog boundary-scan standard does exist). When JTAG is combined with functional testing the analog signals are often handled by the analog instruments used for the functional tests. When JTAG is combined with ICT and FPT systems, often used Circuit analysis & debug in higher volume production, similarly the analog circuitry is handled by the ICT or FPT. To handle the analog circuitry of a board in a stand-alone system Mixed-Signal I/O capabilities are available with JTAG Technologies’ boundary-scan systems (JTAG controllers, I/O modules and software). Background on JTAG boundary-scan With boundary-scan a shift register is added in silicon along the pins (the boundary) of the chip. With each (digital) pin of the chip one or more cells of this shift register are associated. Through these cells one can now control and / or observe a device pin independent of the functionality (core logic) of the chip. The connection between the pins of two, or more boundaryscan chips can easily be verified. All it takes is to drive a 0/1 on an output pin via its bit in the bscan reg and then observe the value seen by the connected input pin(s) via their bits in the bscan reg’s of the chips. This forms the basis of boundary-scan. In this way the connections between bscan devices can easily be verified, even if other non-bscan devices are in between. A very simple example of such device would be a series resistor. When bscan devices are connected to the address, data and control pins of a flash memory then this memory can be written to and read from via the bscan registers of these devices. In this way in-system programming of flash memories via JTAG is possible. Microprocessors often contain special JTAG accessible debug logic for software debugging purposes. This logic may be in addition to a boundary-scan register in the chip. Sometimes, however, a boundary-scan register is not present in those chips. Through the debug logic one has full JTAG control over the CPU core and its busses and everything connected to it. This debug logic can now be used for test and in-system programming purposes (emulative test and programming). JTAG Technologies’ CoreCommanders interface directly with the debug logic of a microprocessor and provide full control over a processor core. CoreCommanders are specific for a processor core, a processor type, or processor family. The functions of a CoreCommander – its API – are independent of the type of processor core. www.electronics-eetimes.com Electronic Engineering Times Europe January 2016 29


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