External Interrupt - Revision history

MacDeath at 20:08, 17 December 2010

2010-12-17T20:08:52Z

← Older revision		Revision as of 20:08, 17 December 2010
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	* [[NMI]] - Non-maskable Interrupts (more commonly used by peripherals)		* [[NMI]] - Non-maskable Interrupts (more commonly used by peripherals)

			[[Category:Programming]]

Arnoldemu: /* External Interrupt (INT Pin) */

2010-06-21T09:10:04Z

External Interrupt (INT Pin)

← Older revision		Revision as of 09:10, 21 June 2010
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	The gate-array interrupt is automatically acknowledged and cleared, so external maskable interrupts should only be cleared explicitly by the Z80 performing an I/O instruction, otherwise they would conflict with the gate-array interrupt and you would not know the source of the interrupt.		The gate-array interrupt is automatically acknowledged and cleared, so external maskable interrupts should only be cleared explicitly by the Z80 performing an I/O instruction, otherwise they would conflict with the gate-array interrupt and you would not know the source of the interrupt.

	~~(This information is mentioned in~~ SOFT968).		SOFT968 Section 11 "Interrupts" mentions this.

	== See also ==		== See also ==

	* [[NMI]] - Non-maskable Interrupts (more commonly used by peripherals)		* [[NMI]] - Non-maskable Interrupts (more commonly used by peripherals)

Arnoldemu: /* External Interrupt (INT Pin) */

2010-06-21T09:05:46Z

External Interrupt (INT Pin)

← Older revision		Revision as of 09:05, 21 June 2010
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	Peripherals that do use external INTs:		Peripherals that do use external INTs:
	* [[Music Machine]] - accordingly to the manual: It can "disable" the internal interrupt, and replace it by external MIDI/ACIA interrupt. ''Unknown if/how it is really doing that, "disabling" the internal interrupt could be probably done only "shortcutting" the INT signal to 5V, which would be a rather aggressive solution - so maybe the manual only meant that software "ignores" the internal interrupt (?) - also, it referred to IRQ, which could eventually also mean NMI rather than INT...? - the Music Machine software isn't in the internet yet, so one can't disassemble/verify this.''		* [[Music Machine]] - accordingly to the manual: It can "disable" the internal interrupt, and replace it by external MIDI/ACIA interrupt. ''Unknown if/how it is really doing that, "disabling" the internal interrupt could be probably done only "shortcutting" the INT signal to 5V, which would be a rather aggressive solution - so maybe the manual only meant that software "ignores" the internal interrupt (?) - also, it referred to IRQ, which could eventually also mean NMI rather than INT...? - the Music Machine software isn't in the internet yet, so one can't disassemble/verify this.''

			When the Z80 acknowledges a maskable interrupt, it will disables acknowledgement of maskable interrupts.
			It will then perform the appropiate interrupt method (as defined by IM0, IM1 or IM2). Interrupts should end with EI:RETI to re-enable maskable interrupts.
			RETI is the special instruction recognised by Z80 compatible peripheral ICs. It is used to control the daisy-chain interrupt mechanism that they have.

			The CPC operating system interrupt handler briefly re-enables interrupts. It does this to effectively detect other interrupt sources. After this the external interrupt vector is jumped to (&003B). This is normally just a RET.
			The gate-array interrupt is automatically acknowledged and cleared, so external maskable interrupts should only be cleared explicitly by the Z80 performing an I/O instruction, otherwise they would conflict with the gate-array interrupt and you would not know the source of the interrupt.

			(This information is mentioned in SOFT968).

	== See also ==		== See also ==

	* [[NMI]] - Non-maskable Interrupts (more commonly used by peripherals)		* [[NMI]] - Non-maskable Interrupts (more commonly used by peripherals)

Nocash: Created page with '== External Interrupt (INT Pin) == The INT signal is internally used by the CPC (triggered at 300Hz, and divided by software to get 50Hz/60Hz Video interrupts). The BIOS does co…'

2010-06-18T19:42:43Z

Created page with '== External Interrupt (INT Pin) == The INT signal is internally used by the CPC (triggered at 300Hz, and divided by software to get 50Hz/60Hz Video interrupts). The BIOS does co…'

New page

== External Interrupt (INT Pin) ==

The INT signal is internally used by the CPC (triggered at 300Hz, and divided by software to get 50Hz/60Hz Video interrupts). The BIOS does contain some provisions for sharing the INT signal with external interrupts. However, most peripherals are using [[NMI]]'s, which don't require to recurse conflicts with internal INTs.

Peripherals that do use external INTs:
* [[Music Machine]] - accordingly to the manual: It can "disable" the internal interrupt, and replace it by external MIDI/ACIA interrupt. ''Unknown if/how it is really doing that, "disabling" the internal interrupt could be probably done only "shortcutting" the INT signal to 5V, which would be a rather aggressive solution - so maybe the manual only meant that software "ignores" the internal interrupt (?) - also, it referred to IRQ, which could eventually also mean NMI rather than INT...? - the Music Machine software isn't in the internet yet, so one can't disassemble/verify this.''

== See also ==

* [[NMI]] - Non-maskable Interrupts (more commonly used by peripherals)