MOVE commands (where the top bit is 0 i.e. bytes <128) will take a given value and put it in the numbered register. You can have up to 1024 commands which can repeat or stop at any point by WAITing for a non existent line I.e. >311 which works at both 50 and 60 Hz. So there is loads of room for creativity and invention. Only the lower 128 Next registers can be written but, this is not an issue as the registers above 127 are mainly used for the accelerator and the Expansion Bus. Register 96 (60h) is the data port to write the instructions. They are two bytes long so you need to write them in pairs with the most significant byte first – not the usual Z80 way but, needed for the way the system works. Register 97 and 98 (61h and 62h) are the controls; the first is the low 8 binary bits of the address to WRITE the instructions, the second contains the bits to control the mode and the top bits of the instruction address. If you change to mode 01b (from another mode like 00b PAUSE/STOP) this also resets where the Copper begins to READ its instructions from back to instruction 0 – in all other cases it will carry on from where it left off last time. The Copper sees the screen starting from the top left pixel of the display area of the screen, this is 0,0. After 32 horizontal values (every 8 pixels) you have the right border, then you have a gap (count of 12) which is where, on an old TV, the spot would be flying back over to the left, then you have the right hand border of the next horizontal line. Note: This zero point is also where the screen "dot" will be when the first *Raster Line Interrupt* occurs. Do not confuse this with normal interrupts on the system which occur in the top left of the whole screen as it is displayed on a monitor or TV. That is actually somewhere in the middle of the bottom right of the Copper view of the screen shown in the diagram below. Exactly at raster line 224 at 60Hz or 248 at 50Hz. Finally when it gets to the bottom of the screen it has the border and then a blank period (8 lines) while the old spot was running back to the top of the screen, then you have a number of lines in the top of the screen area to play with (56 at 50Hz or 32 at 60Hz). To see this change line 1000 for **DATA 128+(45*2),200** and line 1020 for **DATA 128+(45*2)+1,45**. Remember: **1*256+45 = 301**. This diagram will hopefully help to visualise that:  ``` Right H_Blank Left Border Border NextZXOS 3.5MHz > Browser Command Line NextBASIC Calculator Guide More... 1792K 2023-02-05 10:53 ©1982, 1986, 1987 Amstrad Plc. ©2000-2023 Garry_Lancaster v2.08 Logical drives: CM Bottom Border V_Blank ULA IRQ Top Border ``` *Fig. 16 – Copper operation*