Zilog Z08470 User Manual
Page 298
Z80 Instruction Set
UM008007-0715
286
Z80 CPU
User Manual
B generates an interrupt and is acknowledged. The interrupt enable out, IEO, of B goes
Low, blocking any lower priority devices from interrupting while B is being serviced.
Then A generates an interrupt, suspending service of B. The IEO of A goes Low, indicat-
ing that a higher priority device is being serviced. The A routine is completed and a RETI
is issued resetting the IEO of A, allowing the B routine to continue. A second RETI is
issued on completion of the B routine and the IE0 of B is reset (High), allowing lower-pri-
ority devices interrupt access.
A
B
IEI
IEO
IEI
IEO
+
INT