The Z80 CPU is driven by two Two external interrupts drive the Z80. The maskable /INT signal is used 99% of the time as the main communication channel between the Blink and the Z80 CPU for "software"-related data to drive the common hardware events such as the realtime clock, the keyboard, the serial port and battery low eventscondition. The /NMI (non-maskable interrupt) is only used for hardware connection critical events such as power failure or insertion/removal of memory cards in the external slots or the bus-connector (typically sealed of - was never used).
The /INT signal (the actual pin on the Z80 CPU) is seen as a state (enabled or disabled) between the Blink and the Z80 CPU, which is set active (low) when an interrupt signal is communicated from the Blink to the Z80, or high (when no interrupts are available)fired and until being acknowledged. The /NMI is regarded as a pulse that is fired for a hardware-related event. /NMI has not to be acknowledged.
The OZ operating system is using Z80 interrupt mode 1 for maskable interrupts, received through the RST 38H vector. The NMI interrupt is received through the RST 66H vector.
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Mr G, could you please :
1) Remove the link between flapopen and flap. (flapopen is just a state, not an interrupt)
2) Add <--- 1 — between int and sta columns.
3) Add an arrow from sta to z80 with a IN A,(STA) in Z80
4) Bold the /INT REQ and its arrow
5) Enlarge the event and add : Event (5 ms tick, second, minute, serial port byte received, battery low ...)