Nintendo DMG-01 - Game Boy Console Manual page 64

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3.2.4. Stack Pointer Game Boy CPU Manual
command LD SP,$E000. (The Stack Pointer automatically
decrements before it puts something onto the stack so
it is perfectly acceptable to assign it a value which
points to a memory address which is one location past
the end of available RAM.)
The GameBoy stack pointer is initialized to $FFFE on
power up but a programmer should not rely on this
setting and rather should explicitly set its value.
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