Add bit plane fetch orders.

Amiga-Graphics:-Fragments-of-Facts.md

@@ -1,9 +1,9 @@
 Relative to the internal counters:
 
-* NTSC: 262 lines, or 262/263 in interlaced mode; lines are alternately 227 and 228 cycles long;
-* PAL: 312 lines, or 312/313 in interlaced mode; lines are 227 cycles long.
+* NTSC: 262 lines, or 262/263 in interlaced mode; lines are alternately 227 and 228 slots long;
+* PAL: 312 lines, or 312/313 in interlaced mode; lines are 227 slots long.
 
-Each cycle being two processor clock ticks, or one NTSC-rate colour cycle — i.e. one chip RAM access window.
+Each 'slot' being two processor clock ticks, or one NTSC-rate colour cycle — i.e. one chip RAM access window.
 
 Fixed slot per-line cycle access breakdown:
 
@@ -18,9 +18,33 @@ Bitmap data fetch start time is programmable but may not begin earlier than slot
 
 ## DMA Priority
 
-1. Bitplane fetching
+1. Bitplane fetching (or disk/sprite/refresh, per line region)
 2. Copper
 3. Blitter
 4. CPU
 
 The Blitter will yield every fourth slot if BLTPRI in DMACON is clear.
+
+## Bitplane Fetches
+
+### Low-resolution
+
+An eight-slot fetch pattern is followed:
+
+1. [unused]
+2. bit plane 4
+3. bit plane 6
+4. bit plane 2
+5. [unused]
+6. bit plane 3
+7. bit plane 5
+8. bit plane 1
+
+### High-resolution
+
+Four-slot fetch pattern:
+
+1. bit plane 4
+2. bit plane 2
+3. bit plane 3
+4. bit plane 1