Tektronix has just released a new series of oscilloscopes that answer the growing demand for solutions that handle a wide range of general measurement tasks and meet application-specific needs.
One such class of applications is 'serial bus troubleshooting.' Studies have shown that approximately 60% of all electronic design engineers work with low speed serial buses as part of their routine design and debug chores. These designers want tools that can help them selectively capture data from serial streams, and then analyse the packet content and other relevant signals.
In serial bus architectures, a single signal path may carry address, control, data, and clock signals. Tektronix' new oscilloscopes, the DPO4000 Series, make an ideal platform for acquiring and analysing signals from some of today's most common low speed serial buses, including CAN, SPI, and I²C. The DPO4000's underlying bandwidth, sample rate, memory depth, and channel count are well-matched to the job. But most importantly, some innovative new features make serial debug work much easier.
Innovative features
Troubleshooting a serial bus is a process made up of several steps: trigger on a specified serial event; decode that event and interpret its content; and search the data for other occurrences or events of interest. Until now, no single platform has offered all this in an integrated, automated solution. The DPO4000 Series breaks new ground for serial bus troubleshooting with the following features:
* Plug-in application modules enable an engineer to trigger on serial packet content.
* Automated packet decoding and display presents the data in self-explanatory formats that express the content in instantly-readable form.
* Integral data search features find and mark individual serial events, and speed navigation from point to point within the 10 million sample standard waveform memory.
Triggering considerations
During troubleshooting, it is often necessary to confirm that a specific serial packet has been generated or sent across the bus. The packet contains embedded data values and other messages. Common scope functions such as state-triggering or pattern-triggering are not suitable for the purpose - they are meant for parallel data over multiple channels. What is needed is a trigger that can respond to the content of the serial stream.
When equipped with an optional DPO4EMBD application module for I²C and SPI and/or a DPO4AUTO module for CAN, the DPO4000 Series can respond to user-specified trigger conditions including serial data content, address start and stop messages, etc. The trigger has two immediate effects. Firstly, the instrument acquires the event and those surrounding it, to a capacity of 10 million samples. Secondly, the trigger proves that the specified event occurred.
Unique to the DPO4000 Series is a pair of front-panel 'Bus' buttons (B1 and B2) designed to speed serial analysis. In effect, each button selects a preset for a particular type of serial bus. The engineer creates the preset by defining which channels will receive the clock and data signals, respectively, and the thresholds that determine the two binary states (1 and 0). This set-up is re-usable ever after (unless it is overwritten) simply by invoking the appropriate Bus button. No longer is it necessary to repeatedly go to the trigger menu or set thresholds for serial buses. The Bus buttons save time when setting up to acquire serial data, especially when troubleshooting more than one bus configuration.
The beauty of 'Busforms'
A serial packet waveform appears on the oscilloscope display as a train of one and zero values. Trying to decode this information by tracking clock edges and their associated binary data values is cumbersome and prone to errors - yet that is the way many designers have had to interpret their serial bus acquisitions until now.
The DPO4000 Series automatically decodes the binary packets for I²C, SPI, and CAN buses. The display presents not only the waveform, but also a unique 'busform' view. Adapted from the most advanced Tektronix logic analyser platforms, the busform view is a trace made up of symbolic envelopes that align with the packet components on the waveform view. But instead of the individual 1 and 0 binary pulses, the busform typically contains a hexadecimal value representing decoded packet content (a binary format can be chosen if preferred). Now the designer can see at a glance what is happening on the bus without a long, painful, and manual decoding process. Equally important, there are symbols for other events and values: start, stop, address (including read or write status), and missing acknowledge events.
Yet another time-saving decoded view is available: the 'Event Table'. This presents decoded content in a tabular format with a timestamp for every entry, encompassing the entire acquisition. This makes it easy to view every single event on the bus and also enables easy timing measurements between messages. The DPO4000 Series oscilloscopes can produce Event Tables for any of the three serial buses.
Searching for answers
Once an acquisition has been made, it is often necessary to explore the entire record - up to 10 Msamples - to fully debug an issue. Even with the scope decoding each packet, it could still take a long time to manually look through every packet in the acquisition. The best solution would be a tool that automatically searches the existing acquisition data for events that meet user specified criteria: enter the DPO4000's 'Wave Inspector' feature.
In addition to searching on edges, pulse widths, runt pulses, logic conditions, set-up and hold violations, and rise/fall times, Wave Inspector can search on serial bus packets content. For example, it can isolate every CAN message with a specific pairing of address and data values, marking each occurrence with a small indicator symbol on the display screen. Navigating between the marks is a simple matter of pressing the front panel's Previous and Next buttons.
The DPO4000 Series brings powerful serial triggering, decoding, and search capabilities to design engineers looking for solutions to the serial debug problems they encounter every day, setting new standards for efficiency in embedded system troubleshooting.
In effect, the DPO4000 Series oscilloscope is doing what has been done 'by hand' until now - and doing it in microseconds.
For more information contact Channels Measurement Services, 0800 11 7850, [email protected]
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