Does anybody know exactly what the 12v does during high-voltage programming the ATtiny85
The data sheets states...
1. Set Prog_enable pins listed in Table 20-14 to "000", RESET pin and VCC to 0V.
2. Apply 4.5 - 5.5V between VCC and GND. Ensure that VCC reaches at least 1.8V within the next 20 Î¼s.
3. Wait 20 - 60 Î¼s, and apply 11.5 - 12.5V to RESET.
4. Keep the Prog_enable pins unchanged for at least 10 Î¼s after the High-voltage has been applied to ensure the Prog_enable Signature has been latched.
5. Release the Prog_enable pin to avoid drive contention on the Prog_enable/SDO pin.
6. Wait at least 300 Î¼s before giving any serial instructions on SDI/SII.
7. Exit Programming mode by power the device down or by bringing RESET pin to 0V.
Step 3 applies 12v and the way I read it the HV stays there until step 7 when programming is done, but this isn't actually stated (although of course if you power the chip down presumably the 12v goes as well).
It's just as possible that the 12v is no longer required after entering program mode and it is removed.
So to put my question another way, does anyone know if the presence of 12v can be used to detect that the chip is being programmed?