Commodore Amiga - Advanced Topics

You can also stop the Copper by disabling its ability to use DMA for retrieving instruc-
tions or placing data.
The register called DMACON controls all of the DMA channels.
Bit
7, COPEN, enables Copper DMA when set to 1.
For information about controlling the DMA, see chapter 7, "System Control Hardware."
Advanced Topics
THE SKIP INSTRUCTION
The SKIP instruction causes the Copper to skip the next instruction if the video beam
counters are equal to or greater than the value given in the instruction.
The contents of the SKIP instruction's words are shown below. They are identical to
the WAIT instruction, except
that bit 0 of the second instruction word is a 1 to identify
this as a SKIP instruction.
FIRST INSTRUCTION WORD (IRl)
Bit 0 Always set to
1.
Bits 15 - 8 Vertical position (called VP).
Bits 7 - 1 Horizontal position (called HP).
Skip
if the beam counter is equal to or
greater than these combined bits
(bits
15 through 1).
SECOND INSTRUCTION WORD (IR2)
Bit 0 Always set to
1.
Bit 15 The blitter-finished-disable bit.
(See "Using the Copper with the
Blitter" below.)
Bits 14 - 8 Vertical position compare enable bits (called VE).
Bits 7 - 1 Horizontal position compare enable bits (called HE).
20 Coprocessor Hardware