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Questions tagged [interrupt]

For questions regarding processor interrupt signals on retrocomputing hardware

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Why do we need to acknowledge the interrupt from VIC-II?

A page on how to do raster interrupts includes the following code Irq: LDA #7 STA $D020 ; Turn screen frame yellow LDX #90 Pause: DEX BNE Pause ; Empty loop that "...
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Is it possible to switch the interrupt source of the C64 to VIC without changing the IRQ routine?

The ROM IRQ routine at $EA31 is usually trigggered by the timer interrupt 60 times a second. Is it possible to switch the interrupt source to VIC and still use the same routine? If yes, which memory ...
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Does the Intersil 6100 do interrupts differently from other PDP-8s?

As I recall, the original PDP-8 actually does a jsr 0000 when an interrupt happens, so that the interrupt service routine started at address 0001. I think that saves a few gates, since the instruction ...
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What stops an IO device from driving the databus longer than the CPU expects?

For example, consider the case of handling an INT interrupt signal in the Z80. When the CPU makes the IORQ signal active, it expects the requesting IO device to place a vector onto on the databus. And ...
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Why do they use CLI in an IRQ routine?

I am studying an FLI routine in http://codebase64.org/doku.php?id=base:fli_displayer and I noticed that the CLI instruction is being used in this IRQ routine: irq0: pha ... cli ; &...
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Intel 8080 and Altair 8800. 256 I/0 ports, but only 7 free RST (interrupt subroutine) - how it works?

I have looked this video - Altair 8800 - Interrupt Acknowledge Cycle and have few questions (I have read wikipedia Intel 8080 article, Altair 8800 Operator's manual, Charles Petzold "Code" and few ...
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What is the FPD bit on the PDP-10?

When an interrupt happens on a PDP-10 right, as on many other architectures you get the program counter pushed onto the stack. Actually, the program counter includes many status bits in the upper half ...
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How can a C64 interrupt let the KERNAL keep operating?

I am working on a loading screen, and what I wanted was a simple raster trick (just change the border colour on the bottom half of the screen), and also call the KERNAL to load some more data from a ...
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Did the VIC-20 support raster scanline tricks like the Commodore 64?

I've been programming the C64 on/off for over 30 years (wow). However, I have a few VIC-20's I want to program. I never had a VIC-20 as a kid so I haven't had much exposure to them. Am I correct in ...
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Did any Mockingboard game use the VIA timers or interrupts?

There were only a small number of games that supported any of the Apple II sound cards such as the Mockingboard. From those games that used the Mockingboard, did any of them utilize the on-board VIA'...
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Timing interrupts on MS-DOS

On the ZX Spectrum, you get an interrupt every frame. As I recall, the operating system uses this to periodically scan the keyboard and probably other things also, but you can have your own routine ...