if u need precise timing , forget about internal RC oscillator coz it will drift with temp , aging , voltage etc . using 4 pics is a luxury , depending on your application try using a bigger faster pic and use your imagination / skills to make it do the job of all other pics . There is device to device variation for RC oscillator , this is why there is an OSCAL value stored in every device , be careful not to erase the oscal value for eprom windowed version , first thing i do is always read the factory set osc cal value and stick it on the chip itself . feeding the 4 pics from 1 clock is interesting idea , but don't forget u need to make the track between xtal oscillator and pic as short as possible and the higher the frequency the more problems arise by track length . ----- Original Message ----- From: "Lasse Madsen" To: Sent: Sunday, December 02, 2001 2:02 PM Subject: [PIC]: 12C509A Questions. Hi All Im playing with some code for the 12C509A which requires precise timing and i was wondering if the internal RC 4MHz oscillator is as precise (or nearly) as a crystal and if the RC oscillator value varies alittle from device to device as i cannot find this information any where in the datasheet. I've also been looking at the External series resonant crystal oscillator (page 37 in the datasheet) as i have about 4 pics in my applications this would be a cheap way to provide the same clock frequency to all the pics. but some questions arise when i see this schmatic How accurate is the oscillator ? like a RC osc. ? a crystal osc. ? ?? and how many pics can be driven with this osc. ? Thanks for reading ! Best regards Lasse Madsen -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu