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Thread: PIC logic analyzer - digital storage oscilloscope

  1. #11
    Some updates on the project. I have been using IAR EWARM with the STM32VL board. I ran into an issue in trying to achieve the same functionality i.e. capture, transform and send until interrupted. The issue could either be the speed of the GPIO or the way the library handles transforming a port read value into text. I got some blank output. At first i though it was the GPIO not communicating fast enough with the CPU and tried DMA access to store the data read, but still it did not solve the issue i left it aside and went to handle the HM62256A.

    I don't know if its a good sign if you get the same issue some other designers ran into and you are on the right track but this is what happened with the HM62526; I tried to control the memory address ports through a shift register (serial to parallel). The issue was that the speed of capture was worse than with the pic16F628A. Instead of trying to control the memory directly with the pic(that would require 14 address lines, 8 data lines and 3 control lines YES!!!) i am going for something different. I am going to use a pierce oscillator based on a crystal oscillator. This oscillator will then connect to a 14 line ripple counter. I have built and tested the pierce oscillator based on a CD4011 and successfully acheived 4MHZ clock(though dirty but it should do the job). I am waiting for some 74HC00 to arrive which should get me higher in the MHz sampling speed. In the end i am trying to achieve 20MHz sampling speed which sends me to 20MSa/Sec. For capturing the oscillator will run and drive the ripple counter and hence memory addresses. However the issue is reading. The microcontroller will need to be synchronized to the clock for reading. I will either use the pierce oscillator and interrupt it or send a separate clock for reading my experience right now with pic and STM32F have not been very succsful at high speed.

    Otherwise for those of you reading the post , the way the products out there do it is through a CPLD to act as memory controller, i like to learn new things but this is not the time to dive into VHDL programming, buy a CPLD + programmer and take a month to get the whole thing working. Plus the free dev tools from Xilinx and Altera seem highly limited. I'll keep posted
    Last edited by zeus_threat; 03-06-2014 at 06:05 PM.

  2. #12
    some more updates I have been able to get an STM32F103RBT6 to work with USB. I have used the USB HID example provided by IAR and the code runs on EWARM. I had to modify the following files:
    hw_config
    platform_config
    usb_desc

    The reason I used HID is that no driver is needed. There is one major area that's a head ache and it is about the report descriptor. I had to use a tool from usb.org that can generate report descriptors, copied and pasted and it worked.
    Another issue I also ran into is that I cold not get a good c# library to build the pc client. I had to use java and a library called usb4java and now communication flows nicely from the STM32f103 to the pc. The downside is that now I have to rewrite all my logic analyzer functions and interface in java.

    I also completed the code to build a memory controller on a EPM240T100C5 using VHDL. The setup should be as follows:
    Input->Buffer->HM62256<-EPM240T100C5<-STM32F103RBT6->USB->PC

    The STM will control the CPLD which in turn will control the RAM. Next step is to build a pierce oscillator to act as signal clock for the EPM240 to control the memory address. I will keep posted. Any input is welcome

  3. #13

    PIC Logic Analyzer

    Hi zeus_threat,
    I found your project and I am very interested in building one. I will follow your progress, and when I start to build my own I will keep you posted here.
    Regards,
    mike

  4. #14
    Hi glad to see someone here. If you are interested in looking at some "DIY vintage" way of doing this Dave Jones from EEVBlog built one way back in 1990s its somewhere in his blog including the magazine article he wrote https://www.youtube.com/watch?v=iwRhvhKJlzs

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