need some help

[Thelen]

i wanted to try some programming on the atari 2600 but I don't understand this :

 

my intention was to see at screen line 10 byte number 3 of pfdata1, but i get it over the whole screen

 

i don't see what i do wrong, I compare Y with 10, so only if Y=10 then the pfdata byte 3 will be drawn at line 10 i thought.

 

 

LDY #191

 

ScanLoop

 

STA WSYNC

 

CPY #10 ; compare y with 10

BNE nop0 ; not 10 ? goto nop0

LDX #3

LDA PFData1,x ;byte 3 from pfdata

STA PF1

LDA #$FA

STA COLUP0 ;color FA

nop0

DEY

BNE ScanLoop

 

 

thanks, TheleN

[DanBoris]

Two possible problems. First are you clearing PF1 at the start of the frame? If not then it will always display the same pattern. Also, if you want to only display on that single line you will have to clear PF1 after that line.

 

Dan