If you MOVE 0,0 (i.e. Write something to a Read Only Next Register like Register 0) then the Copper does nothing for a short duration (a NOP in Z80 terms) so you can wait for a more accurate moment to overcome the fact you only have 55 horizontal positions to wait for i.e. every 8 pixels on the screen. You can write to the Copper as it is running because it keeps a separate track of its READ instruction address to the address you are using to WRITE. WARNINGS: Be careful as the *NextZXOS Screensaver* uses whatever palette is in place so if you have any border effects running they will still be visible and could cause a CRT screen to experience a burn-in effect. This is worth bearing in mind if you are writing software not to leave static images around too long! If you try to write to a Next Register at the same time as the Copper then this might cause a conflict – don't worry; the Copper will win and the display will be OK but, your program command may fail. So some care is needed to manage the two systems. Turning off the Copper while you make Next Register affecting changes in *NextBASIC* is a good idea. That includes things like the **PALETTE** command for example. If you are using machine code you will need to use some form of flag and remember what the Copper might be doing at a specific time. In the above program for example, it is possible the Copper STOP in the first two lines will fail if you run it a second or third time to change the colour and will not reset the write address, so you will write after the list already there and your new one will never be reached. You could get around that by repeating the first two lines as it is unlikely to fail twice so shortly after the last attempt and has no effect if it does run twice. ### Exercises 1. Write a procedure to write a STOP command twice in a row so that you can make sure the Copper is stopped when you need to in your programs. 2. Draw a Spectrum Flash on the right hand side border by changing the palette colour five times – make sure the last time is back to your real paper/border colour. Hint you can use one or more WRITE 0,0 as a very short delay. 3. Write a program that controls two spaceships using the sprite defined, one going horizontally, while the other vertically on the screen 4. Enhance the above program with a memory based *Layer 2* animation running in the background