Hi all!

I'm a bit confused with loopy's 2005 doc:

The first line is completely clear to me
2000 write:
t:0000110000000000=d:00000011
d is written to $2000 (use nametable 3) so the adress in the temp adress value is $C00 (offset of the 3rd nametable).

But now - line 2 confuses me completely:
2005 first write:
t:0000000000011111=d:11111000
x=d:00000111

I suppose that d is written to $2000 again (or is that maybe wrong??). If it's true the nametable adress is now $2000 (or 0000 in the t). So why is the 11111 there? If I'm wrong and d is written to $2005 i don't understand why the 11111 is in t either. (it looks like the bits in d are mirrored and transfered to t).

Hope somebody can help me out of this -):)

Regards Martin

I was in the same position a while back. Your problem is that Loopy's shorthand is a bit confusing. I'll see if I can explain it a bit better. The important thing to note is that the long strings of 0's and 1's are a bit mask. A 1 indicates that that bit position is affected, and a 0 indicates that it is not.

2000 write:
t:0000110000000000=d:00000011
This means that when a byte of data 'd' is written to $2000, the lower 2 bits of 'd' will be placed into bits 10 and 11 of the temporary register 't'.


2005 first write:
t:0000000000011111=d:11111000
x=d:00000111
This means that when a byte of data 'd' is written to $2005, and it is the first write to $2005, then the upper 5 bits of 'd' willl be placed into the lower 5 bits of temporary register 't'. In addition, the lower 3 bits of 'd' will be placed into a separate register which Loopy named 'd'.

The names 't' and 'd' are from Loopy's document, and those registers are used by the ppu to refresh the screen. I hope this helps.

Ahhhh!!!!

Now everything is completely clear - thx very much m8!

regards Martin