Real Time Clock

I found the thread dated April 1st 2004, in a Google Groups search for SPI RTC.

Thanks, David

Hi, Be careful if you choose DS1305 !!! I'm waiting for 100 pcs since 1.5 months...

Depending on your battery current budget, MCUs may not be a good fit. They normally use a lot more power than a standard RTC which is designed to run from a watch battery for years, just like watches.

One exception is the MARC4 (4 bitter) from Atmel and a line of 4 bit MCUs from EM owned by Swatch (surpise!). These are both designed to run from a watch battery at just 1 or 2 uA currents.

Hi David,

Some folks have suggested a uC with realtime clock. Here is a good one: MSP430. Has an internal clock and when shut down with only this RTC running it consumes just a few micro amps.

Regards, Joerg

What about the MSP430? I have one in an application that runs a 32KHz watch xtal and wakes each second to count time, using an average current of 0.7uA. The advantage of the MCU is that you can make it do things when it wakes other than just increment the time. My app wakes on NVRAM IButton contact and records its time (32bit seconds or YYYYMMDDHHMMSS) into the button - reliably! (CRCs, scratchpad readback, all the good stuff).

Clifford Heath.

You could try Maxim's MAX6902. It is an SPI compatible RTC, with timekeeping current consumption of 400nA at 2V. It also operates from 2v -> 5.5V. However it comes in a TDFN form factor (3mm x 3mm x 0.8mm).

Accidently flick it with the tweezers and it's gone.

However I understand that Maxim's delivery schedules leave something to be desired. Sample deliveries are ok though. Today I received a MAX1811 Li+ charger ic about a week after I requested a sample.