| ??? 01/23/05 17:55 Read: times Msg Score: +2 +1 Good Answer/Helpful +1 Informative |
#85628 - Reset Switch Issue Responding to: ???'s previous message |
Mahmood:
If you have the reset switch contacts connected right to the processor RESET pin along with say a resistor to bias the RESET pin to the non-reset state when the switch is open....then you are susceptable to problems. The switch as you know is a bouncy element and will have many many momentary openings and closings as you activate the switch and then release it. If on the release the last "bounce" of the switch creates a reset pulse that is too narrow for the microcontroller you can see that the chip will not reset properly. The solution for this is to change over to an external reset supervisor chip that has provisions for a reset switch input. Another possibility is to debounce your reset switch with a NC, NO, and COM FORM-C switch connection to a SET-RESET type flip flop. Yet another choice may be to try to buffer the switch via an RC network through an 'HC14 type of chip with hystersis. Do note that many times if you use a chip like ah 'HC14 to drive the RESET input to the microcontroller, having an active driver to both the high and low state, that is is necessary to place a resistor of say 4.7K in series with the output of the chip. This is needed because some microcontrollers will drive a signal out on the RESET pin for either the power on reset cycle or for a watch dog reset cycle. Michael Karas |
| Topic | Author | Date |
| Strange Reset Problem | 01/01/70 00:00 | |
| Is it RC circuit | 01/01/70 00:00 | |
| No RC | 01/01/70 00:00 | |
| Reset Switch Issue | 01/01/70 00:00 | |
| a possibility | 01/01/70 00:00 | |
| No Luck! | 01/01/70 00:00 | |
| Glitches? | 01/01/70 00:00 | |
| I can guess what may be wrong if... | 01/01/70 00:00 | |
| try this | 01/01/70 00:00 | |
| PCB is the only suspect left! | 01/01/70 00:00 | |
| EMI problem | 01/01/70 00:00 | |
which derivative | 01/01/70 00:00 | |
| Power on reset | 01/01/70 00:00 | |
| Is there reset input? | 01/01/70 00:00 | |
| doesn't matter | 01/01/70 00:00 | |
| But what is the problem? | 01/01/70 00:00 | |
| just fixed similar | 01/01/70 00:00 | |
| sounds like wiring problem | 01/01/70 00:00 | |
| It wouldn't be would it? | 01/01/70 00:00 | |
| But Mahmood said, it's not the LCD! | 01/01/70 00:00 |