HALT mode and power consumption

boris · ‎2008-04-06

Posted on April 06, 2008 at 19:01

boris · ‎2008-03-29

Posted on March 29, 2008 at 17:56

I have made pretty simple timer using ST microcontroller with LCD display. I noticed strange behaviour regarding power consumption in HALT mode.

I use: ST7FLIT19BY1 (16 pins) and SW Visual programer ID 2.0.5, Jun 8 2007 and STICK programmer.

Clock source is resonator 4MHz, device is normally in Slow mode.

I program the device via 10 pin ICP conector.

I have measured the current consumption under different settings in OPTION byte and get following results:

16 pin device, LVD ON: 0.68mA in Slow mode / 0.30mA in HALT mode

16 pin device, LVD OFF: 0.63mA / 0.19mA

20 pin device, LVD ON: 0.59mA / 0.13 mA

20 pin device, LVD OFF: 0.54mA / 0.01 mA

Why I get the expected low current consumption only with Â»wrongÂ« setting (20 pins device instead 16 pin)?

All other things works normally regardless Â»number of pinsÂ« setting.

I am a confused since I am not sure may I use Â»20 pinsÂ« setting for my controller which definitely has 16 pins?

Thanks a lot.

seb13_colin · ‎2008-04-03

Posted on April 04, 2008 at 07:01

Hello Boris,

The Package OPT bit is used to put the ''unused IO'' (I mean the pins present in the 20 pins package and not in the 16 pins package: PA1, PA3, PB5, PB6) in a fixed state. For example, when the 16 pin package is selected the unused IOs are tied to fixed voltage (I guess VCC) internaly. So, on the 16 pins package, the unused IOs must be configured as floating input. If it's not the case, for example if you configure the unused IOs as output push pull at '0' (VSS), you will see a consumption due to this conflict of level (VCC tied by the OPT bit and VSS applied by the push pull output). If you want to reduce your part consumption you have to configure the unused IOs (on the 16 pins package) as floating input.

I hope it will help you.

Best Regards,

Seb

boris · ‎2008-04-06

Posted on April 06, 2008 at 19:01

Dear Seb,

thank you very much for your reply. You were absolutely right. As soon as I defined ''virtual'' I/Os like floating inputs the power consumtion dropped down even at 16 pin configuration in Halt mode. Problem solved!

I think this is one of the rare things which are not explained in the datasheet?

Best regards.

Boris