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Name: Trace Hook

Hook Pointer Block Address: 9BA8

Hook Enable BCALL: 4FF3

Hook Disable BCALL: 4FF6

Hook Call BCALL: 4FF9

Hook Active Flag: 0, (iy + 36h)

This hook allows you to change the actions that happen when tracing a graph.

Using the Hook

These different values, passed in a, determines what the hook should do.

  • 0: Unknown what this is used for, but it's called between the a=1 and a=4 hookcalls.
    • b: contains the function that will be graphed y1=01 .. y0=0A or x1=01.. x6=06 or r1=01 .. r6=06 or u=01 .. w=03.
  • 1: The trace cursor will move.
    • Zero flag: clear to abort the move.
  • 2: The trace cursor wants to move outside the screen and thus the graph will be (partially) redrawn.
  • 3: The trace cursor blinks.
    • Zero flag: Clear to stop the blinking
  • 4: The trace cursor is (re)drawn
    • Zero flag: Clear to abort the drawing of the cursor. (The blinking pixel in the middle will still blink at the position the cursor wasn't drawn)


This documentation is probably incomplete.