reset circuit implementation on AVR32 microcontroller based design

Discussion in 'Embedded Systems and Microcontrollers' started by cobrasv, Jan 4, 2011.

  1. cobrasv

    Thread Starter New Member

    Jan 4, 2011
    3
    0
    HI,

    I have been designing a microcontroller based circuit. it consists of an AVR32 uC, a wiznet w5100 hardwired ethernet controller and another PHY IC as the main devices. All these devices need to be reset when the board is powered up.
    2 ways i could use are : a. use a reset IC that will simultaneously reset all devices on powerup OR b. since the uC anyway has a built-in POR, i could use its GPIO pins to reset the other devices.

    for option b., this would mean the other devices reset only after the uC has initialised after its own reset. so, is it ok to use this technique? could the delay in resetting the other devices cause trouble?

    this is my first time at microcontroller based design.

    Thanks in advance
     
  2. Bosparra

    Member

    Feb 17, 2010
    79
    3
    The easiest would be an RC circuit to reset all devices simultaneously. A 10K resistor from Vcc to a 100n cap connected to ground. Connect the reset line between the resistor and the cap.
     
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  3. Papabravo

    Expert

    Feb 24, 2006
    10,140
    1,789
    Check the specs on the AVR32 device you are using. The schematic of the EVK-1100 (AT32UC3A0512-0ESAL) has a 10K resistor to Vcc, and a 100 nF capacitor in parallel with a momentary pushbutton switch to GND. The node between the resistor and the capacitor is connected to pin 23 on the processor. The same node is connected to the Ethernet PHY (DP83848I) pin 29 and several other peripherals so they all use the same quasi-analog RESET signal.
     
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  4. cobrasv

    Thread Starter New Member

    Jan 4, 2011
    3
    0
    I have gone through the EVK. That implementation is ok when i want to manually reset the system. but will it help at initial power-up?
    From Bosparra's post, i think the same circuit is placed across the switch in EVK, ie 10K to Vcc and 100nF to Ground which will keep the reset line active low till the cap charges... YES, i gues that solves the problem :)

    thank you sirs
     
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