Parameters for DrawPicture, read and written through IY. BASIC only POKEs the picture number here; *DrawPicture_Third and *DrawPicture_Thirds are always FF in the snapshot, so the routine takes the screen third and the number of thirds from the picture record.

The flags at DrawPicture_Flags:

Bit	Relating To
00	Pixel data order (set: rows; clear: columns)
02	Set while a run of repeated bytes is being written
03	Set while the attributes are being drawn

Parameters for DisplayFrame. BASIC POKEs them relative to "ins".

Work space used by DisplayFrame for the screen and buffer character offsets of the frame.

Parameters for ScrollWindow. BASIC POKEs them relative to "scr".

Half-character flag for PrintString.

Work space used by the routines above to hold the stack pointer while they switch to a temporary stack.