| ??? 09/06/07 07:23 Read: times |
#144072 - this is relatively complicated... Responding to: ???'s previous message |
... and one of my stories of spectacular failure.
The rough outline is, have a powerdown detection circuit with output connected to an input (maybe interrupt) pin of '51; then if the '51 senses powerdown occuring, it should place all peripherals in "safe" position (e.g. if you have motors connected you should stop them), then go to powerdown mode (stop oscillator); plus of course you need the battery backup circuit (nowadays, a lithium cell plus a schottky diode (and maybe a protection resistor in series) will do). The powerdown should sense the input voltage for the voltage regulator, and/or you should make sure the VCC stays on the capacitors high enough (for the micro and the peripherals) until you succeed to perform the powerdown operation, otherwise the battery gets drained too quickly. The gotcha is in the wakeup. In a classical '51, there is no other means of exit from powerdown mode than a reset. So, you MUST NOT reset during low power, but a reset pulse of a proper length MUST be generated when the power is restored. This was the tricky part we could not get quite right... Another gotcha is the lifetime of the battery and the hassle with its replacement if it dies. If the application has to be truly bulletproof, you even need to implement battery voltage measurement and warn the user if the battery is about to die... JW |
| Topic | Author | Date |
| Memory of AT89C2051 after reset | 01/01/70 00:00 | |
| this is relatively complicated... | 01/01/70 00:00 | |
| Why no reset during low power? | 01/01/70 00:00 | |
| during active reset the oscillator is running... | 01/01/70 00:00 | |
| power back up? | 01/01/70 00:00 | |
| Oh, certainly... | 01/01/70 00:00 | |
| thanks | 01/01/70 00:00 | |
| alternatives | 01/01/70 00:00 | |
| options? | 01/01/70 00:00 | |
| my way of doing this... | 01/01/70 00:00 | |
| Then jus a RAM chip would work | 01/01/70 00:00 | |
| wouldn't it be easier and safer with serial EEPROM | 01/01/70 00:00 | |
| Maybe | 01/01/70 00:00 | |
| why not FRAM | 01/01/70 00:00 | |
| Combination of Technologies.... | 01/01/70 00:00 | |
| SRAM | 01/01/70 00:00 | |
| I don't think so | 01/01/70 00:00 | |
| this is not matter of "thinking"! | 01/01/70 00:00 | |
| OK, an another gotcha | 01/01/70 00:00 | |
| to Jan | 01/01/70 00:00 | |
| no | 01/01/70 00:00 | |
here is the best chip for u! | 01/01/70 00:00 |