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Hi! I've got an exercise regarding 8085 interrupts.
I have a 8085 microprocessor whose memory addresses from 0024h to 003Fh are the following
24 C3
25 00
26 FF
27 00
28 C3
29 00
2A F5
2B 00
2C C3
2D 80
2E F5
2F 00
30 C3
31 00
32 F6
33 00
34 C3
35 8O
36 F6
37 00
38 C3
39 00
3A F7
3B 00
3C C3
3D 80
3E F7
3F 00

I'm asked which are the ISR addresses of the h/w interrupts TRAP, RST5.5, RST6.5 and of the s/w interrupts RTS5, RST6 and RST7.
I am confused, as I thought that all those interrupts have their addresses, eg. TRAP is always located in 0024, RST5.5 in 002C etc. Could someone please explain to me what I'm supposed to look for, in order to solve the exercise?

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Member Avatar for gusano79

I'm asked which are the ISR addresses of the h/w interrupts TRAP, RST5.5, RST6.5 and of the s/w interrupts RTS5, RST6 and RST7.

I am confused, as I thought that all those interrupts have their addresses, eg. TRAP is always located in 0024, RST5.5 in 002C etc. Could someone please explain to me what I'm supposed to look for, in order to solve the exercise?

I think the exercise is asking you to give the address of the interrupt service routine itself, not the offset of that address in the interrupt vector table. Looks like you know where to find these offsets already, so all you have to do is report the ISR address and you're done. Unless I missed something :)

Member Avatar for ambageo

I think the exercise is asking you to give the address of the interrupt service routine itself, not the offset of that address in the interrupt vector table. Looks like you know where to find these offsets already, so all you have to do is report the ISR address and you're done. Unless I missed something :)

Thank you for your response. I'm afraid that I haven't figured out what's the difference between the actual ISR address and the offset of that address in the interrupt vector table. Let's take the TRAP interrupt vector table address. It is 0024.What does this exactly mean and how is it connected to the ISR address? I'm really not trying to find someone to do my homework for me, it's just that I haven't found something relevant to read and understand...

Member Avatar for gusano79

I'm afraid that I haven't figured out what's the difference between the actual ISR address and the offset of that address in the interrupt vector table. Let's take the TRAP interrupt vector table address. It is 0024.What does this exactly mean and how is it connected to the ISR address?

You're right; the 8085 jumps straight to 0024h when TRAP happens. But all of the other interrupts live really close as well, so there's not much space to do anything useful there. There is enough space, though, to execute another jump to a much larger chunk of code. I think you're being asked to find the address of that code. Disassemble the bytes at 0024h in your assignment, and I bet you find a JMP instruction.

it's just that I haven't found something relevant to read and understand...

Yeah, there really isn't a lot of useful introductory information about the 8085 out there in the intertubes--mostly it's technical references or super-simplified overviews. :(

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