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Reset circuit on Prop1 Protoboard USB — Parallax Forums

Reset circuit on Prop1 Protoboard USB

agsags Posts: 386
edited 2013-04-07 13:29 in Propeller 1
Will someone explain the principle behind the NPN BJT with base connected through a series capacitor to the DTR pin of the FTDI (USB interface) chip on the Propeller Protoboard USB? I presume that it operates with a short pulse on the DTR pin causing a transient which propagates through the capacitor, causing Q1 forward bias and conducting to pull RESET low. After the transient forward bias is gone, allowing RESET to float. This also isolates the DTR pin from VSS when the reset button is pushed. Right?

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2013-04-07 13:22
    When the DTR line goes high, the capacitor charges via the 10K pull-down resistor and the transistor turns on briefly creating a RESET pulse (to ground). The end of the 10K resistor connected to the capacitor becomes positive relative to ground causing the transistor to conduct. DTR is isolated from the RESET line by the transistor and the capacitor.
  • agsags Posts: 386
    edited 2013-04-07 13:29
    That's what I (tried to) say. Thanks, makes sense.
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