Commodore Amiga A500 Technical Reference Manual page 209

*NOTE BFD = Blitter finished disable. When this bit is true, the
Blitter Finished flag will have no effect on the Copper. When this bit
is zero, the Blitter Finished flag must be true (in addition to the rest
of the bit comparisons) before the Copper can exit from its wait
state, or skip over an instruction. Note that the V7 comparison
cannot be masked.
The Copper is basically a 2-cycle machine that requests the bus only
during odd memory cycles (4 memory cycles per in). This prevents
collisions with Display, Audio, Disk, Refresh, and Sprites, all of which
use only even cycles. It therefore needs (and has) priority over only
the Blitter and Micro.
There are only three types of instructions: MOVE immediate, WAIT
until, and SKIP if. All instructions (except for WAIT) require 2 bus
cycles (and two instruction words). Since only the odd bus cycles are
requested, 4 memory cycle times are required per instruction (mem-
ory cycles are 280 ns).
There are two indirect jump registers, C0P1LC and C0P2LC. These
are 18-bit pointer registers whose contents are used to modify the
program counter for initialization or jumps. They are transferred to
the program counter whenever strobe addresses COPJMP1 or
COPJMP2 are written. In addition, C0P1LC is automatically used at
the beginning of each vertical blank time.
It is important that one of the jump registers be initialized and its
jump strobe address hit, after power up but before Copper DMA is
initialized. This insures a determined startup address and state.
DIWSTRT
D1WST0P
These registers control the Display Window size and position, by lo-
cating the upper left and lower right corners.
BIT# 15,14,13,12.11,10,09,08,07,06.05,04,03,02,01,00
USE v7 v6 v5 v4 v3 v2 vl v0 h7 h6 h5 h4 h3 h2 h1 h0
DIWSTRT is vertically restricted to the upper % of the display
(v8 = 0), and horizontally restricted to the left 3A of the display
(h8 = 0).
DIWST0P is vertically restricted to the lower 1?? of the display
(v8=/ = v7), and horizontally restricted to the right 'A of the display
(h8 = 1).
DDFSTRT Display data fetch start (horiz.position)
DDFSTOP Display data fetch stop (horiz.position)
206
Display window start (upper left vertical-hori-
zontal position)
Display window stop (lower right vertical-
horizontal position)