Dear Andy

From datasheet under 'absolute maximum ratings' table:

1) MFRC500 - DC supply voltages is -0.5V(min) and +6.0V(max)

2) P89C66X - Voltage on EA/VPP pin to VSS is 0V(min) to +13.0 V(max);
Voltage on any other pin to VSS is –0.5V(min) to +6.5 V(max)

Note: On my board I only use this two chips as a core component, others are passive supporting component like Xtal resistors, etc.

Thus, does this mean I can connect 6V directlly to VCC without causing any harm to my board?

Thanks
Parif