# VPP-First Entry Mode

To enter Program/Verify mode via the VPP-First Entry mode, the following sequence must be followed:

1. 1.Hold ICSPCLK and ICSPDAT low.
2. 2.Raise the voltage on MCLR from 0V to VIHH.
3. 3. Raise the voltage on VDD from 0V to the desired operating voltage.

The VPP-First Entry mode prevents the device from executing code prior to entering the Program/Verify mode. For example, when the Configuration Byte has already been programmed to have MCLR disabled (MCLRE = 0), the Power-up Timer disabled (PWRTE = 0) and the internal oscillator selected, the device will execute the code immediately. VPP-First Entry mode is strongly recommended as it prevents the user code from executing. See the timing diagram in Figure 1.

Figure 1. Programming Entry and Exit Modes – VPP-First and Last