] I've been wondering. Except for the opcode and the timing, is there a
] difference between RET and RETI? I know RETN does iff1=iff2, RET. But my
] documentation on RETI only says that the program knows the interrupt is
] finished.
Quoted from a book about the Z80, describing the RETI instruction:
'The Zilog-periferal-chips can see that an interrupt routine has ended by the
fact that the ED and 4D opcodes appear on the databus during the M1 cycle.
When using a daisy chain, this instruction makes sure that nested interrupts
with different priorities are handled in the proper order, by resetting the
IEO of the device for which the interrupt service routine has just finished'
As you can understand from the above description, using the RETI instruction
does not make much sense in a standard MSX computer. The standard MSX
computer simply does not have any hardware device monitoring the bus to see
if the RETI instruction has been executed. Though, one might build a
cartridge or a hardware extension with such a hardware device...
Kind regards,
Alex Wulms
--
Alex Wulms/XelaSoft - MSX of anders NIX - Linux 4 ever
See my homepage for info on the *** XSA *** format
http://www.inter.nl.net/users/A.P.Wulms
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