How to keep date and time after shut down power in STM32F429iDisco?

[Linda]

Posted on June 10, 2015 at 23:34

Hi,

We want to add a cell battery to keep time and date. but in the schemaitcs, Pin 1 and Pin 6 in STM32F429iDisco for VBAT alredy connect to +3V.

What we can do?

Thanks a lot

[l239955_stm1]

Posted on June 11, 2015 at 07:39

Use 3V voltage regulator. Other idea is used PWM signal to regulating voltage level (switching transistor)

[waclawek.jan]

Posted on June 11, 2015 at 08:54

According to the 429DISCO schematics, Pin6 (VBAT) is connected to VCC through a 0 Ohm resistor (jumper) R52. Remove it and us its pad to connect a battery - I admit it's not the nicest thing to do but it's workable.

I don't understand what did you mean by Pin1 (PE2).

JW

[Linda]

Posted on June 11, 2015 at 13:25

Dear waclawek,

The pin 1(VBAT) of U2(STM32F103C8T6) connected to 3v, I do not need to do anything?

If so, that seems a good idea.

Thanks

[waclawek.jan]

Posted on June 11, 2015 at 13:35

The 'F103 is the debugger (STLink). You don't need to connect battery to it.

JW

[Linda]

Posted on June 11, 2015 at 14:37

Dear paroulek,

I try the power stop mode and power standby mode, the LCD is on, it take a lot of battery.  Is there any way to shut down the LCD completely when MCU in standby mode?

Thanks

[Linda]

Posted on June 11, 2015 at 14:41

Thanks JW.

Now I connect a cell battery to Pin 6, the board and hold time and date, but keep the reading of power off. When I turn it on, the time is not updated.

What I should do?

[Tesla DeLorean]

Posted on June 11, 2015 at 14:43

No, you can't turn display off.

As indicated you'd remove the resistor/link on the VBAT side, and provide a battery.

You'd also want to add an LSE crystal and capacitors.

[Linda]

Posted on June 11, 2015 at 14:53

Dear clive1,

Where I should add the LSE crystal and capacitors? is PC14,PC15? 

 32.768Hz  crystal is good?

Thanks

[Tesla DeLorean]

Posted on June 11, 2015 at 15:14

Where I should add the LSE crystal and capacitors?

Top side of the board, north of the display. Review schematic and manual. There may be some other zero ohm or solder bridge changes also, and I think these are explained in the manual.

Generally with STM32 designs you need to clock the RTC via the LSE as it's part of the low-power domain, and suspend into the battery backed operation.

[waclawek.jan]

Posted on June 11, 2015 at 16:20

See UM1670, 4.11.2 OSC 32 KHz clock supply, ''Oscillator on board (from X2 Crystal)''

JW