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Problematic RESn Line - Preventing multiple Propellers from playing nice. — Parallax Forums

Problematic RESn Line - Preventing multiple Propellers from playing nice.

WossnameWossname Posts: 174
edited 2013-01-08 00:23 in General Discussion
Does anyone here know of some authoritative information about how the RESn pin should be handled on a "real world" Propeller circuit? The Propeller manual seems to use the RESn pin as a receive antenna when the Prop Plug is not attached.

Sometimes when I build a circuit, the RESn pin seems to cause me some problems - even touching the pin with my finger will cause the Prop to reset... even if there's a 4K7 pull-up resistor on there.

I want to be able to use the Prop Plug to program my circuit but I also want to run it __robustly__ when the Prop Plug is not connected. Has anyone got any hints about how to do this?

I have tried to use various combinations of pull-up/down resistors and these have varying success and often simply cause Prop Plug programming to fail.

Is there a "known good" way to handle the RESn line when in-system programming is desirable?

Documentation seems a tad sparse on this subject.

Comments

  • WBA ConsultingWBA Consulting Posts: 2,934
    edited 2013-01-07 16:26
    You have something very odd going on there. I have never done anything with a RESn pin in any setup I have done except connect it to a propplug or other USB programming circuit. Never had any pullups.
  • prof_brainoprof_braino Posts: 4,313
    edited 2013-01-07 16:29
    What kind of power supply are you using? I whack my test rigs around and seldom get an issue, but I been having fun with marginal (I think) power supplies
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2013-01-07 20:45
    Aslo, don't forget that the RESn pin is pulled up internally only if BOEn is pulled low.

    -Phil
  • cgraceycgracey Posts: 14,255
    edited 2013-01-07 20:57
    I bet it is static discharge that is triggering the reset with the 4.7k pull-up attached. Try putting a 0.1uF cap between RESn and VSS. That will not interfere with the Prop Plug.

    It might be best to put a 47K pullup on RESn, along with a 0.1uF cap to VSS, then drive RESn via a 4.7k. That way, the 4.7k/cap combo can squash any spikes from ESD.
  • WossnameWossname Posts: 174
    edited 2013-01-08 00:19
    I'll try those suggestions but I'm not convinced it's ESD. I've had this trouble at work also on one Prop board and that was running from a good quality PSU with good regulation on the board itself plus proper ESD handling measures (grounded ESD mats, wrist straps etc).

    Perhaps it would be possible to revise future versions of the Prop manual to have the example schematic amended to include more explicit handling for things like smoothing caps, pullups and anti-ESD measures? If not in the schematic itself then in the text that accompanies it.
  • WossnameWossname Posts: 174
    edited 2013-01-08 00:23
    Phil Pilgrim (PhiPi) wrote: »
    Aslo, don't forget that the RESn pin is pulled up internally only if BOEn is pulled low.

    -Phil

    Indeed, the schematic in the manual connects it directly to VSS. I do want the BOEn enabled anyway, it is a sensible thing to do IMO.
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