topic Re: Real Time Clock on S08QE in 8-bit Microcontrollers

Real Time Clock on S08QE

DK1BN — Thu, 01 Oct 2009 14:54:50 GMT

Hi,

did someone using the QE Series as a Real Time Clock with 32kHz Xtal?

How is the power consumption? Or should we better use an external dedicated IC for this purpose. We have experience with CDP68HC68T1 and using SPI. We need Date/Time functions.

Regards

Walter

Re: Real Time Clock on S08QE

tonyp — Thu, 01 Oct 2009 21:18:42 GMT

We've been using a software calendar clock with several QE[32/128] designs (w/ 4MHz crystal) and the overall experience is great. In our case, to support the clock, the MCU is powered from a CR2032 battery during power loss. The system wakes up every second when in this mode (it could be every minute if clock accuracy is less important than power consumption). Under normal operation, it wakes up every 1msec to support the RTOS task switching, and various other timing functions. Total PCB power consumption for clock maintenance alone is somewhere around 2uA (if I remember correctly, it's been a while), which for our application(s) is perfectly fine.

There are so many factors that affect acceptable (clock battery) consumption for each application, it's not easy to give specific recommendations. For example, clock power consumption is far more important in e-agenda type devices, where they spend most of the time in low-power mode keeping time but you want battery replacements/recharges to be as few as possible, than in always-on systems which only need protection from occasional and temporary (and, usually, no more than few-hour long) power outages.

Message Edited by tonyp on 2009-10-01 05:23 PM

Re: Real Time Clock on S08QE

donw — Fri, 02 Oct 2009 01:53:17 GMT

If using an RTC IC, Check out the DS3234 RTC. I find it the near perfect timekeeping

solution. No xtal, no tweeking, and long term accurate...

Re: Real Time Clock on S08QE

DK1BN — Mon, 05 Oct 2009 12:58:36 GMT

Thanks for ypur suggestions. we will have a try using S08QE8 for such a purpose. I hope we will be better than 2 uA for power consumption using 32 kHz Xtal.

Again thanks.

Walter