Glitch on P1[0] at POR and XRES

Question: After POR or XRES event, P1[0] goes high for some time. Why is it so?



All GPIO pins in the PSoC are in the HighZ state during POR or XRES reset events.  But Pins P1[1] and P1[0] are ISSP pins and respond differently to a POR or XRES event than other IO pins.

At power up, the internal POR causes P1[0] to initially drive a strong high (1) while P1[1] drives a resistive low (0). After 256 sleep oscillator cycles (approximately 8 ms), the P1[0] signal transitions to a resistive low state. After additional 256 sleep oscillator clocks, both pins transition to a high impedance state and normal CPU operation begins.