Why do I need a programmable delay between Vdd and Vpp (Vdd-to-Vpp)?
Answer
Most target devices enter programming mode by applying the Vdd voltage first, followed by Vpp. Many target PCBs include large capacitance (typically 100–1000 µF or more) on the Vdd line, which causes the supply voltage to rise slowly.
A programmable Vdd-to-Vpp delay ensures the correct sequence — Vdd first, then Vpp — even when Vdd takes longer to stabilize.
