Logic analyzer
- Thread starter fernando_g
- Start date
I own one and find it very helpful. The software is very intuitive and easy to use - often people forget that the hardware is ony one half of the equation, and that the software makes or breaks the overall usability. Since the analyzer streams the captured data into the PC the available memory depth is virtually unlimited so often I don't even bother setting up sophisticated trigger conditions - just log a few seconds of data and then zoom into the place where the action happened.
The main limitation are the sampling speed (24 MHz max) and number of channels (8) which can be an obstacle when debugging e.g. a larger FPGA design (jn case you ever get into such a situation
- but for things like RS-232, SPI, I2C, one-wire etc. that analyzer is a huge help and the price is very reasonable. (again, it's not just the - nicely made - hardware, but also the software you are paying for). For these four protocols the software offers built-in protocol decoders - much easier than trying to decipher a scope trace.
Wolfgang
The main limitation are the sampling speed (24 MHz max) and number of channels (8) which can be an obstacle when debugging e.g. a larger FPGA design (jn case you ever get into such a situation
- but for things like RS-232, SPI, I2C, one-wire etc. that analyzer is a huge help and the price is very reasonable. (again, it's not just the - nicely made - hardware, but also the software you are paying for). For these four protocols the software offers built-in protocol decoders - much easier than trying to decipher a scope trace.Wolfgang
fernando_g
Senior Member
Exactly my thoughts...these protocols are ubiquitous around microprocessors, and one really needs to be able to read the actual data stream to properly troubleshoot devices.
I also own a Saleae LSA and have found it a useful development tool. I can remember high cost LSA that always seemed to take more time to set up than to operate, but the Saleae user interface is very well designed. The speed performance is more than adequate for most PICAXE based systems but may struggle a bit on the faster X2 versions.
Hi MFB, I'm not quite sure the X2 Picaxes are any more tasking on the Saleae LA than any other Picaxe - while they are somewhat faster (~2x) they are still very slow compared to a "real" microcontroller, and also compared to the maximum sample rate of the Saleae. The fastest signals you can produce - and that is true for X2 parts as well as other Picaxes - are PWM (at a few MHz), RS-232 harware serial (up to ~250 kHz), and hardware SPI (up to a few MHz). All well within the 24 MHz sample rate of the analyzer. I have successfully used the Saleae to debug the serial side of a FT232R USB-to-serial converter setup running at up to 1 Mbaud.
Ah yes, the wonderful logic analyzer.
Long in the distant past, I wrote a self-paced training package for the Tektronix 7D01 logic analyzer (for the 7000 series oscilloscopes). Even built a "trainer" (digital clock with important leads brought out to a reverse-mounted wire-wrap IC socket) - which emulated working on the backplane of an electronic telephone switching system. After I field-trialed the trainer and the written course materials (with good reviews from the techs who participated), the engineers decided that field analysis would need an analyzer with more channels so they specified a BioMation analyzer. Having learned a great deal about analyzers and how to use them while writing the training package, I became the organization's unofficial logic analyzer expert: "To capture the data when pin 3 is high, pin 17 is low, and there is a state transistion on pin 5 or 12, connect these leads and set these switches..."
If I needed a logic analyzer now, I would looks first at the PC-based units such as the one in the link. Meanwhile, my multi-channel tool is a Tektronix 2247A 4 channel scope, found for $100US when a local company shut down ther R&D unit. The calibration is a couple of years out of date, but with free-running clocks on most of the PICAXE circuits I build, relative timing (are the SDA and SCL leads changing state appropriatel?) is more important than to-the-microsecond values.
John
retepsnikrep
Senior Member
I concur with Womai and without the Saleae Logic analyser I would have struggled with my various RS485 projects. It's not that expensive either IMHO. It's a great bit of kit.
I might like a few more data formatting options with the export functions so it's easier to manipulate when loaded into excel.
A direct load/export into excel might be nice.
I might like a few more data formatting options with the export functions so it's easier to manipulate when loaded into excel.
A direct load/export into excel might be nice.