| ??? 12/11/06 14:02 Read: times |
#129281 - I use only external watchdog / brown-out detection Responding to: ???'s previous message |
Richard said:
How, then, should one generate a bidirectional reset, for those MCU's that both receive and drive the reset pin, as I mentioned earlier with reference to the watchdog timer? I do not use the internal watchdog of micro and I don't use the internal brown-out detection, either. I think the best results can be expected by using an external watchdog and external brown-out detection. So, I nearly always use the MAX1232. Richard said:
How can one determine that the MCU's oscillator is stabile? Maybe one should rule out using a crystal, and use a complete oscillator instead. Those have spec's that tell us how long from Vcc to stabile output. One could, after all, count, say, 4K (e.g. with 74HC4040) counts from the oscillator and then release the RESET. The internal Pierce oscillator was originally designed by INTEL to show a fast start-up time. 10msec is enough to have it entirely started (a nearly instantanenous rise of Vcc assumed). So, with a reset time of 100msec you should always be on the safe side. Nevertheless, you should never use a cheap crystal for this Pierce oscillator, because this can result in start-up problems, caused by high internal dampening of quartz (high equivalent series resistance). You might also want to have a look at the Intel's famous application note "AP-155": http://apps.intel.com/scripts-u...=Developer Kai |
