| ??? 08/14/07 13:34 Modified: 08/14/07 13:38 Read: times |
#143257 - Not only... Responding to: ???'s previous message |
Jan said:
The ONLY reason why Intel and the cloners specified VCC rise time is to make the crappy RC reset work. And they insist on the crappy RC reset to seem cheap enough. Another reason is the start-up issue of built-in oscillator. With the rather poor crystals fabricated in the early days of 8051, they worried, that the oscillator could not start-up with a too slowly power-up. The dU/dt kick of power-up is THE relevant motor to start the oscillator and the rise time should be about less than the time the oscillator needs to fully start-up. That's the reason, why a rise time of less than 10msec is stated in the original datasheets of Intel. But today, the crystals are so good, that the oscillators even start with a much more decayed power-up. That's the reason, why the 10msec rule disappeared from the datasheet copies of Philips, etc. Kai |
