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running at 50MHZ with 3V — Parallax Forums

running at 50MHZ with 3V

kwanhkkwanhk Posts: 3
edited 2006-04-05 15:34 in General Discussion
Hello everybody!

I have make a project using SX28 running at 50MHz with 3V power supply. Before I started the project, I tested that·the SX28·can run·with·the Murata·50MHz ceramic resonator·at·3V supply (using a simple flashing LED programme). During the development, I test everything with SX-Key debugger. However, as I completed the code for my project and tested it along, I found that it can't run properly at 3V. The power supply has to be more than 3.8V·in order to make it·run properly.

I have already used a 0.1uF ceramic and 47uF eletrolytic cap for power bypass.

What is the problem? What can I do to maintain the configuration of 50MHz, 3V and using a ceramic resonator. Or is there any solution that enable me to maintain 50MHz at 3V?

Comments

  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2006-03-30 06:37
    Are all your parts really rated for that low a service?

    Is your oscillator failing to run?
    If so, it may be the oscillator settings, it may be the lack of a resistor in parallel with it [noparse][[/noparse]usually 1meg].
    The shift to a lower voltage may under-power the resonator which lacks·fine tuning.

    My personal goal is to operate at 3.3volts.
    It seems that many ICs are tolerant to the range from 3.3 to 5.5 volts, so I can buy for either. Also, if you consider diodes usually have 0.7volts of voltage drop, I suspect that lower voltage ICs must stay about an absolute minimum of about 4 x 0.7volts = 2.8volts. You are getting quite close to that. Being higher gives you more leeway as you actually have more power to correctly drive the system.

    Trying to bounce off the absolute minimum may force you to sort and select parts from a larger population as production runs do vary.

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    ······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan

    Post Edited (Kramer) : 3/30/2006 5:50:46 PM GMT
  • BeanBean Posts: 8,129
    edited 2006-03-30 12:10
    Please post your device settings.
    You may need a BOR26 setting on the device line.
    Or as Kramer has pointed out a different OSC setting.

    Bean.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    "SX-Video·Module"·available from Parallax for only $28.95 http://www.parallax.com/detail.asp?product_id=30012

    "SX-Video OSD module"·available from Parallax for only·$49.95 http://www.parallax.com/detail.asp?product_id=30015
    Product web site: www.sxvm.com

    Available now! Cheap 4-digit LED display with driver IC·www.hc4led.com

    "I reject your reality, and substitute my own." Mythbusters
    ·
  • NateNate Posts: 154
    edited 2006-03-30 17:24
    Kramer,

    I have to ask, how in the world did you come up with:

    "Also, if you consider diodes usually have 0.7volts of voltage drop, I suspect that lower voltage ICs must stay about an absolute minimum of about 4 x 0.7volts = 2.8volts."

    Nate
  • kwanhkkwanhk Posts: 3
    edited 2006-04-05 06:28
    I am using the SX28AC/DP and the Murata 50MHz ceramic resonator delivered together with tool kit.
    I have tried bith OSC1 and OSC2

    other settings are:
    internal feedback resistor enabled
    BOROFF
    TURBO
    STACKX
    WATCHDOG
  • BeanBean Posts: 8,129
    edited 2006-04-05 11:15
    Change "BOROFF" to "BOR26" and add "OSCHS2".
    Bean.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    "SX-Video·Module"·available from Parallax for only $28.95 http://www.parallax.com/detail.asp?product_id=30012

    "SX-Video OSD module"·available from Parallax for only·$49.95 http://www.parallax.com/detail.asp?product_id=30015
    Product web site: www.sxvm.com

    Available now! Cheap 4-digit LED display with driver IC·www.hc4led.com

    "I reject your reality, and substitute my own." Mythbusters
    ·
  • kwanhkkwanhk Posts: 3
    edited 2006-04-05 14:55
    Dear Bean,

    Thank you very much for your advice!

    After changing from "BOROFF" to "BOR26", the MCU can run at low as 3.2V.

    But I don't understand why the brownout level affect the operation of my programme. Can you tell me why? Thanks a lot.
  • BeanBean Posts: 8,129
    edited 2006-04-05 15:15
    It has to do with the rise time of the power supply. Without a BOR setting the processors tries to run at very low voltages and gets "hung-up" for some reason. Some power supplies work without the BOR setting, but I always use it to be safe.

    Bean.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    "SX-Video·Module"·available from Parallax for only $28.95 http://www.parallax.com/detail.asp?product_id=30012

    "SX-Video OSD module"·available from Parallax for only·$49.95 http://www.parallax.com/detail.asp?product_id=30015
    Product web site: www.sxvm.com

    Available now! Cheap 4-digit LED display with driver IC·www.hc4led.com

    "I reject your reality, and substitute my own." Mythbusters
    ·
  • Paul BakerPaul Baker Posts: 6,351
    edited 2006-04-05 15:34
    It has to do with the level of bypass capacitors used, they take time to charge, and the SX cant run at 50MHz at the lowest voltage it can run at (~2.7V), so if the normal waiting period before execution occurs and the voltage isnt high enough to permit 50 mhz operation the SX will hang. The BOR setting will force the SX into reset (plus some additional time) until the voltage levels rise enough to permit full 50mhz operation.

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