Calculating VRAM Addresses

But there is a quicker mental maths way to do this that I use to calculate VRAM addresses. Let's just say you wanted to write to VRAM address $C62E:

Boundary 0  <=>   $0000-$3FFF
Boundary 1  <=>   $4000-$7FFF
Boundary 2  <=>   $8000-$BFFF
Boundary 3  <=>   $C000-$FFFF

Firstly, find what $4000 byte range the address slots into (Boundary 3). Then you subtract it by that boundary's starting value (in this case, $C000, giving $62E).
After that, you add the subtracted value by $4000 (Which signifies the VRAM write mode, giving $462E). Now we can put the VDP command together:

$462E <- That will be your first word of the command, which essentially tells you what relative offset from the boundary to start writing.

$462E 00 <- Next two bytes are ALWAYS 00. The VDP doesn't use them!

$462E 00 03 <- Your final two bytes are the boundary your address falls into, in this case 3.

Combined, you get the final VDP command $462E0003, which will write to the VRAM address $C62E.