Output from PortB & PortD at the same time on Uno r3

Projects General Guidance
2

For truly simultaneous, you will have to preload an external shift register as multiple instructions (74HC595 for example), and then use shared latch pin to move output from incoming shift register to the output latch.

digitalWrite (latchPin, LOW);
SPI.transfer(lowBits);  // two 74HC595 with daisy chained data line
SPI.transfer(highBits);
digitalWrite (latchPin, HIGH);  //latchPin updates all 16 outputs at same time