pixels not updating when instructions are stepped through 

I am running this code which is supposed to set 5,5 on but it only does it when I run it in bulk and not by stepping through 
```
ldi r1 240 
ldi r2 5
str r1 r2
ldi r1 241 
ldi r2 5
str r1 r2
ldi r1 242 
str r1 r0 
ldi r1 245
str r1 r0 
nop
nop
nop
nop
hlt
```