Copper Control High Byte
From SpecNext official Wiki
| Number | $62 |
|---|---|
| Readable | No |
| Writable | Yes |
| Short Description | Holds high byte of Copper control flags. |
| Bit | Function |
|---|---|
| 7-6 | Control mode |
| 5-3 | Reserved, must be 0 |
| 2-0 | High three bits of Copper list index (value 0-2047) |
When "Control mode" bits are identical with previously set ones, they are ignored - allowing for index change without restarting currently running Copper program.
Copper has internally 10 bit "program counter" register (CPC), going through 0-1023 values, executing Copper instruction from the list at memory position (CPC*2). This will cause the Copper program to loop automatically. To "halt" program (avoiding possible loop), use WAIT instruction with non-existent horizontal line, like "WAIT 63,511 = 0xFF, 0xFF".
To change control mode, the new value must differ from previous, the possible control modes are:
| Bits 7-6 | Control mode |
|---|---|
| %00 | STOP Copper (CPC is kept at current value) |
| %01 | Reset CPC to 0 and START Copper |
| %10 | START Copper (does resume at current CPC) |
| %11 | Reset CPC to 0 and START Copper, reset CPC at each video frame at (0,0) (top left pixel of PAPER area) |