Questions tagged [interrupt]
For questions regarding processor interrupt signals on retrocomputing hardware
16votes
4answers
4kviews
Did DOS on the early, slow machines ever fail to handle interrupts timely, and what happened if it did?
DOS on the 8088 had to process interrupts and return. If a higher-priority interrupt occurred, the current handler was pushed and the higher-priority interrupt was serviced.4.77 million seems like a ...
- 4,763
4votes
1answer
371views
Intel 8275 CRTC not generating interrupts. Any way out?
According to the 8275 datasheet, the interrupts are enabled always after the Enable Interrupts command is issued. As the retrace counters are always running, even before the component initialization, ...
- 2,298
4votes
1answer
587views
Hardware and CPU-generated interrupt mapping at BIOS boot time
What is the mapping of hardware interrupts (all the IRQs and NMI) and CPU-generated interrupts (such as division by zero) to real-mode interrupt vectors at BIOS boot time, i.e. at the time the BIOS ...
- 5,499
10votes
0answers
411views
What is the "K09" referenced in MS-DOS sources? Is it the same as the IBM PC Convertible?
In the MS-DOS v4.00 sources (which I forked for lMS-DOS upon the 2024 April free software release) the msbio module has several references to a machine called "K09", for instance in https://...
- 1,747
7votes
1answer
465views
How does the Z80 NMI edge detection work?
The Z80 user manual (um0080.pdf) is basically useless for finding out many details about NMI. The diagram is broken and there's no mention that it's edge-triggered rather than level-triggered like INT ...
- 486
5votes
2answers
314views
How do I wait for end-of-frame (VSYNC) on a TRS-80 models 1 and 3?
I've been looking at various documentations, and couldn't find a clear answer. I understand the Model 1 has no interrupt from the video generator, but I'm hoping there's at least a way to busy-wait ...
- 2,830
12votes
2answers
2kviews
Why does the BRK instruction set the B flag?
On the 6502, the brk instruction is a software interrupt. Like any other interrupt, it pushes the status word to the stack and then the program counter, before transferring control to an interrupt ...
- 41.2k
14votes
2answers
1kviews
Is there any way to read current Interrupt Mode in Z80 machine code?
Is there any way to read current Interrupt Mode in Z80 machine code?Official Z80 datasheet mentions IMFa/IMFb registers which keep the mode value.Thank you
- 297
2votes
1answer
507views
What was the 6502's reset behaviour when the RDY pin was low
How does an original 6502 behave if the ready pin is being held during a reset/power-on event?Would it pause CPU start-up entirely, delaying when some or all of the 6 internal cycles are executed? (...
- 5,317
42votes
4answers
9kviews
Did any MS-DOS program ever use the System Request interrupt?
As I remember, the SysRq key generated a special, unique interrupt (not an ordinary keyboard interrupt). It was supposed to let the user interrupt any process in a multitasking situation and return ...
- 4,763
5votes
1answer
666views
Did the i186 use interrupt 6 for invalid opcodes?
I don't recall where from but at some point I was under the impression that the Intel 186 processor used interrupt 6 for invalid opcodes.However, there's the HP 95LX that uses a NEC V20. NEC V20/V30 ...
- 1,747
7votes
1answer
324views
Does the PDP-8/E service an interrupt after any instruction, or after instructions not referencing memory only?
While researching this answer about incrementing the program counter, I found something I thought was a little odd in the FETCH state flow diagram, which is figure 3-8 of the PDP-8/E & PDP-8/M &...
- 41.2k
21votes
10answers
10kviews
Was there any computer since about 1960 without interrupt support?
The invention and spread of interrupts in the 1950s is reasonably well known but I am curious: were there any systems after which didn't support them?
- 1,342
12votes
0answers
278views
Anyone know of older mentions of the word "trap" for software interrupts than the IBM 704 manual from 1955?
I've dug into the origin of the word "trap" in computer engineering. The older documented mentions of the term I can find, is the "trapping mode" in the IBM 704, specifically in ...
- 849
12votes
2answers
2kviews
ZX Spectrum interrupt handling: maskable and NMI
Is there a skeleton for handling the interrupt on the ZX Spectrum? Can I read it?I need the ZX Spectrum to handle an interrupt from a device and I have no idea where to start from.I like the idea of ...
- 469
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