] >Though, when you build such a device you should make sure
] that
] > you only have one such device in your computer. If you put a second =
] one in
] > the second cartridge slot for example, you will get bus conflicts if =
] they
] > generate an interrupt at the same time... Or to be more precise, if =
] they
] both
] > generate an interrupt before the Z80 acknowledges it (the interrupt =
] does
] not
] > get acknowledged as long as the Z80 is in DI mode...)
]
] IMO this is not completely true. I found the device at the end of this =
] email in a book about Z80 assembler. It has 4 switches each combined =
-- part about building device cut-out --
With which part of my message do you disagree?
I agree that if you build your device, insert it into a cartridge slot and
use your program, you can have four indepedent interrupt generators
controlled by this single device.
But what if you add a second one into the second cartridge slot? Both devices
can and will write at the same time to the databus, thereby causing
bus-conflicts.
On a computer that has been designed from scratch to work with interrupt
vectors (like the original IBM PC), the 'cartridge' cards are not directly
attached to the interrupt of the CPU but to an interrupt controller, like the
one you just described. Therefore, the system architecture of such a computer
is such that you will not get these conflicts. At least, not at that level.
However, the MSX standard prescribes that cartridges are directly connected
to the interrupt input of the CPU. So, you can perfectly add two different
interrupt controllers into your computer causing conflicts which each other.
Which is exactly the reason that IM2 is not supported in the MSX standard.
Kind regards,
Alex Wulms
Kind regards,
Alex Wulms
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