| ??? 01/12/12 06:35 Read: times |
#185443 - You can do it, though you may not want to Responding to: ???'s previous message |
Erik Malund said:
If you can find a solid specification for exactly how long the RESET/nRESET pin on your particular MCU must be held high or low, then, with the aid of a calculator and a schmidt-trigger inverter, you can fabricate a circuit that produces a sufficiently long active-high/low pulse of appropriate voltage and stability during both power-up/power-down conditions and occasional brownouts, should they occur.
no, you can't a) a schmitt trigger requires a minimum Vdd and thus the output is unknown at low Vdd b) there is no way in hades a RC circuit with or without a schmitt trigger can generate a reset at power down Erik Erik Malund said:
If you can find a solid specification for exactly how long the RESET/nRESET pin on your particular MCU must be held high or low, then, with the aid of a calculator and a schmidt-trigger inverter, you can fabricate a circuit that produces a sufficiently long active-high/low pulse of appropriate voltage and stability during both power-up/power-down conditions and occasional brownouts, should they occur.
no, you can't a) a schmitt trigger requires a minimum Vdd and thus the output is unknown at low Vdd For MCU's with Vdd defined as +5 volts, which is still a goodly number of them, one can certainly use gates specified for operation down to 3 volts. b) there is no way in hades a RC circuit with or without a schmitt trigger can generate a reset at power down there is no way in hades that a RESET during power-down, specifically, during the sometimes very long and slow decay of Vdd, can guarantee anything. Stopping the oscillator to the MCU will do that, however, yet no supervisor or other reset generator seems to have attempted that. Erik As they say, "Where there's a will there's mourners." If you really want to do it, you'll find a way. I've seen at least one CMOS schmidt gate that operates down to 2.5 volts. Where there's one, there's more ... RE |
| Topic | Author | Date |
| AT89ISP Reset Pin Issue | 01/01/70 00:00 | |
| If you want a positive-going RESET ... | 01/01/70 00:00 | |
| no, you can't | 01/01/70 00:00 | |
| You can do it, though you may not want to | 01/01/70 00:00 | |
| The AT89ISP will expect active-high RESET | 01/01/70 00:00 | |
| Try to run the initialize target command... | 01/01/70 00:00 | |
By the way... | 01/01/70 00:00 |