Zilog Z08470 - Manual (Page 300)

Z80 Instruction Set UM008007-0715
288
Z80 CPU
User Manual
That address begins an interrupt service routine that ends with a RETN instruction. Upon
the execution of a RETN instruction, the contents of the former Program Counter are
popped off the external memory stack, low-order first, resulting in stack pointer contents
of
1000h . The program flow continues where it left off with an op code fetch to address
1A45h .