M24SR GPO creating a 1s square wave no matter what i do

[Luke Iliffe]

Posted on May 30, 2018 at 20:58

Hi all,

     I have a really weird problem, no matter what I do the M24SR creates a 1s sqaure wave on the GPO pin and when I say 1 second it is excatly 500ms off and 500ms on.  I have set the GPO to be HIGH Impedance for both RF and I2C comms and it still does it, I have killed all power to it and then re-applied it and same difference. Its like I've managed to discover a test mode which is undocumented as far as I can tell. Has anyone found this before and if so how can I get the device out of this mode?  please find first bit of the system file data attached

Thanks for looking

Luke

[JP Miller]

Posted on May 31, 2018 at 11:04

Dear Customer,

there is no such feature of automatically generating a 1s square wave from the M24SR tag series.

When programming the byte 0x0004 of the System File (corresponding to GPO) to 0, the GPO remains high impedance no matter what the activity is on the M24SR RF or I2C interfaces.

May you please explain what you are trying to do with the GPO pin?

In usual cases, the GPO pin is connected to a pull up resistor connected itself to VCC power supply. Is that the configuration you are having?

If you are not using the GPO for any matters, you might want to try to write the 

byte 0x0004 of the System File (GPO) to 0x55, so that it will only toggle if specific RF or I2C commands (StateControl) are sent to control the GPO State. Without sending any such commands, the GPO will not toggle at all.

Have a nice day,

Best regards,

JP

[Luke Iliffe · Accepted solution]

Posted on May 31, 2018 at 12:47

so I found the issue, the GPO line goes into PC13 of an STM32F030 and somehow when setting the time of the RTC using the HAL functions the Calibration function of the rtc was switched on. this created a 1 second pulse even with the STM being held under reset. Which mislead me to think it was the M24SR.

Thanks for the reply

Luke