Splitting the Atom

page 4

II. The FOR / NEXT Stacks

240				24A		Variable 1=A, 2=B, etc.
24B				255	LSB	Step size stack
256				260
261				26B
26C				276	MSB
277					LSB	Terminal value stack
282
28D
298					MSB
2A3				2AD	LSB	NEXT return address - i.e. where FOR was.
2AE				2B8	MSB
	^ |
	15	= FOR / NEXT Stack Pointer

Each new FOR command increments the FOR/NEXT stack pointer to point at the data relevant to this loop, viz, the location of the FOR, the terminal value, the STEP size and the variable used.

A similar map can be drawn for DO/UNTIL and GOSUB/RETURN loops, though there are obvious differences. See Chapter 3: RAM Usage.