tmm41256p-15 DRAM tester

[Homer_79]

Here is the datasheet, for the tmm41256p-15

https://4donline.ihs.com/images/VipMasterIC/IC/TOSC/TOSCS32892/TOSCS32892-1.pdf

I'm doing some work with DRAM, so I thought i'd start with something simple.

This is basically what I want to build, but I thought I would start by understanding how the software works first.
http://www.chronworks.com/DRAM/
http://www.chronworks.com/DRAM/memoryTest.ino

I can follow the code through and it kind of makes sence. Its just an array of 512x512 bits.
But how the decoding of the 9 bits is something im struggling with.

  // First write all Zeros to DRAM
 
  digitalWrite(DIN, LOW);
 
  for(col = 0 ; col < 512 ; col++)
    {
    for(row = 0 ; row < 512 ; row++)
      {
      PORTB = row & 0x3f;            // Write out ROW address ---- Why set all 6 bits to 1's?
      PORTC = ((col & 0x1c0) >> 6) | blue;                              ---- what does this line do?
     
I thought portc would start off at bits 0, not the upper 6

I'm just starting out with arduino, so forgive me learning curve.

many thanks