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islandcontroller/a600_level7_switch.md

Created July 12, 2025 17:24
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Amiga 600 Level 7 Interrupt (NMI) Switch
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a600_level7_switch.md

Amiga 600 Level 7 Interrupt (NMI) Switch

A short modding guide for adding a level 7 interrupt switch to your A600.

Materials

  • 3x 1N4148 (or similar) diodes
  • 2 pos. pin socket and matching header
  • Momentary switch or push button
  • Insulated wire, heat-shrink tubing, superglue

Assembly

  • /IPL0 (Interrupt Priority Line 0, active-low): connect to R953A pad close to U3.
  • /IPL1 (Interrupt Priority Line 1, active-low): connect to R953B pad close to U3.
  • /IPL2 (Interrupt Priority Line 2, active-low): connect to R953C pad close to R152B.
  • Connect other socket pin to square GND pad next to trapdoor edge connector.
  • Momentary switch SW1 plugs into the socket and pulls D1..3 cathodes to GND when triggered.

Usage

Pushing the switch triggers a level 7 interrupt (NMI - non-maskable interrupt) in the 68000 CPU by pulling all three /IPL signals to GND. Some IDEs assign a NMI handler to trigger a debugger breakpoint. This interrupt can also be used to enter HRTMon.

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