# 8051 / EFM8LB1 / programming via C2 after PCON0.STOP := 1?

Yesterday I wanted to see, how much power my EFM8LB1 uses, when it has just this firmware with bootloader disabled:

.org 0
ljmp 1$1$:
orl (REG01CN), #8
orl (PCON0), #2


Today I found, that I cannot access it via C2 anymore. I tried keeping it in reset when powering on and then sending C2 commands... without success...

How can I fix it without dumping the MCU and soldering a new one?

How does that EFM8LB1 decide if the reset means "now we do C2" or "now you run the reset ljmp"?

• check the datasheet Apr 23, 2021 at 21:35
• @jsotola i did. but: the datasheet is not very clear about my questions. after the reset it seems like the MCU starts to turn everything off, before i can send the "halt core" byte. but i dont understand why, because i only wait less than 5usec after reset and the code execution starts allegedly after appr. 50usec. Apr 24, 2021 at 5:52