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  • Joined: 03 Aug 2017
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  • Location: Munich
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interrupt modes IM0 and IM2
Post Posted: Wed Aug 16, 2017 12:49 pm
Hi,

I wonder if there is any SMS cartridge or device (connected to the extension port) which uses IM0 oder IM2, all the neccessary connections should be available.

If there is no official SW/HW, that use IM0/2, maybe someone used it for some homebrew project (e.g. extending the SMS to a home computer with keyboard, floppy disc etc.).

Bye,
Knaeckebrot
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  • Joined: 05 Jul 2017
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  • Location: Cornwall, United Kingdom
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Post Posted: Wed Aug 16, 2017 2:53 pm
As I understand it they both require external hardware?
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Post Posted: Wed Aug 16, 2017 6:50 pm
Some games use the other interrupt modes for bad reasons (not doing the canonical di; im 1 on startup), but I can't remember an example.
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Post Posted: Wed Aug 16, 2017 11:06 pm
matt wrote
As I understand it they both require external hardware?


(I'm not sure if I understand you correctly)

You definitely need some logic in hardware (which the SMS lacks). To use IM0/2, the hardware has to specifically implement the Z80-specific interrupt procedure, e.g. putting a "RST xy" or the LSB of the interrupt vector table address on the bus.

Just looking at the pins, each external accessory including the cartridges should be able *in principle* to use IM0/2 (as intended by Zilog).
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  • Joined: 17 Nov 2015
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Post Posted: Sat Aug 19, 2017 1:49 am
Knaeckebrot wrote
To use IM0/2, the hardware has to specifically implement the Z80-specific interrupt procedure, e.g. putting a "RST xy" or the LSB of the interrupt vector table address on the bus.


Yes and this is easy to achieve for im2 if you use the z80 peripherals to do the interfacing like the pio, ctc, sio, etc.
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