topic Re: MC9S08SH8 BKGD pin at power up in 8-bit Microcontrollers

MC9S08SH8 BKGD pin at power up

robertogiovinet — Thu, 26 Oct 2017 11:49:22 GMT

Hello community

I've a problem. I use this microcontroller since a lot of year, but lately there's something wrong. I use BKGD pin as I/O pin, so at the beginning i set SOPT1 register

SOPT1 = 0b00000000;

Sometimes when I power up the circuitry, the pin show a 2.3V voltage (I use 5V as power supply) and my program does not start. I can't understand why! The circuit I use is very similar to one I use in other product in which this fact has never show!

I use an external resistor as pullup to 5V on the BKGD pin as in the image I've attached. Then a 1K resistor goes to a red led that goes to GND.

Does anybody know how is it possible? Where I'm wrong?

As I told before, this scheme is used since some years but only now I've problems.

Re: MC9S08SH8 BKGD pin at power up

tonyp — Thu, 26 Oct 2017 14:21:51 GMT

You seem to have an external pull up. Are you sure you don't also have an pull-down in the MCU (i.e., bit PTAES4=1)?

Re: MC9S08SH8 BKGD pin at power up

robertogiovinet — Thu, 26 Oct 2017 14:47:47 GMT

No pull down setted or enabled in MCU. PTAPE = 0b00000000;

As I mentioned before, I've a situation as in the image below: a pullup (10K) to 5V, a resistor (1K) with a red Led diode. I know that the diode can be polarized from 5V and 11K, but i don't know why it never happened in the past!