At 11:04 AM 10/16/00 +0200, you wrote: >> Van: Jinx >> Aan: PICLIST@MITVMA.MIT.EDU >> Onderwerp: Re: [EE]: I2C Real Time Clock >Yes, but I'm switching between two voltages, one for the "active" state of >the whole device (5.0 volts), one for the "dormant" state (device powered >down, only the clock keeps on running off a NICAD or similar). The only number I see listed in the data sheet related to this is the "typical" figure of 0.2ppm/100mV, which would be typically 5ppm if it is linear (and I would definitely verify *that* with a good reciprocal frequency meter) for a change from 2.4V -> 5V, maybe double or triple this for a realistic "maximum". Is that the kind of thing you are seeing? If the change is more, I'd suspect the bypassing of the chip power. OTOH, if this is about the magnitude of change you are seeing, maybe you could reduce the voltage swing by some method. The I2C is ok, with reduced noise immunity, so long as the Vdd for the chip is > 2.5V. With a matched pair of Schottky diodes (in an SOT-23-ish package) plus an LM317 and a couple of 1% resistors (or maybe a TL431 if the voltage is right), you could probably reduce the swing by 10:1 or more at a fairly modest cost. Check that the reverse leakage of the Schottky diodes isn't too high for the 5V-off condition, particularly if you have to operate at high temperature. Best regards, =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= Spehro Pefhany --"it's the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com Contributions invited->The AVR-gcc FAQ is at: http://www.bluecollarlinux.com =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.