] >On the MSX interrupts the interrupt ends with a EI:RET. (No RETI, it has no
] >use).
]
] But it has a reason I forgot. What's the actual effect of RETI? What are
] the differences with an EI/RET? And with an EI/RETI?
It is mainly a feature for hardwaredevelopers that use the Z80 as a
microcontroller. They can build a circuit that monitors the databus and
M1-pin to see when the interruptroutine has finished. Just check for the RETI
opcode during the Z80's M1 cycle... Ofcourse, the programmer of the firmware
should have the discipline to always use the RETI instruction at the end of
the interruptroutine. And the programmer should not use the RETI instruction
in any other place.
This feature is not used in the MSX.
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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