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'ISA bus IRQ interface'
1997\09\28@221620 by Sean Breheny

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Hello All,

I'm building a generic 8 bit fast bidirectional I/O card for the 8-bit ISA
bus to interface with various circuits including PICs. I would just like to
know if someone could set me straight about how to generate IRQs. Can I
just pulse  the appropriate IRQ pin (i.e. IRQ5 for IRQ 5 )? If so, what are
the max/min lengths for this pulse. Is there some type of acknowledge
procedure, or is that it? Do I need to synchronize this pulse with the ISA
clock or other signals? Do I need to make sure that I don't pulse this at
the same time as another card?

Thanks,
Sean

Sean Breheny,KA3YXM
Electrical Engineering Student

1997\09\28@224055 by Peter Wintulich

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Extract From the AT Technical Refrence:

IRQ's
"An interupt request is generated when an IRQ line is raised from low to high.
The line must be held high until the microprocessor acknowledges the interupt
request (Interupt Service routine). Interupt 13 is used on the system board and
is not available on the i/o channel. Interupt 8 is used for the real-time
clock."

I also found that the standard printer port dose not conform to this, as it has
not got any latching device in the interface. It just passes the ACK pulse from
the printer's ACK pin. This pulse width is typicaly 5us.

1997\09\28@224912 by Sean Breheny

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At 12:12 PM 9/29/97 +0930, you wrote:
>Extract From the AT Technical Refrence:
>
>IRQ's
>"An interupt request is generated when an IRQ line is raised from low to
high.
> The line must be held high until the microprocessor acknowledges the
interupt
> request (Interupt Service routine). Interupt 13 is used on the system
board and
> is not available on the i/o channel. Interupt 8 is used for the real-time
> clock."
>
>I also found that the standard printer port dose not conform to this, as
it has
> not got any latching device in the interface. It just passes the ACK
pulse from
> the printer's ACK pin. This pulse width is typicaly 5us.
>

Thank you for the information, but I still have one question, how does the
microprocessor ack the IRQ? I am looking at a diagram of the ISA bus and I
don't see any IRQ ack pin or anything like that.

Thanks again,
Sean

Sean Breheny,KA3YXM
Electrical Engineering Student

1997\09\28@230544 by Alan G. Smith

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----Original Message-----
From: Sean Breheny <spam_OUTshb7TakeThisOuTspamCORNELL.EDU>
To: .....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU <PICLISTspamKILLspamMITVMA.MIT.EDU>
Date: Sunday, September 28, 1997 10:50 PM
Subject: Re: ISA bus IRQ interface

>Thank you for the information, but I still have one question, how does the
>microprocessor ack the IRQ? I am looking at a diagram of the ISA bus and I
>don't see any IRQ ack pin or anything like that.
That is up to you.  Generally in your ISR you do an IO write to a memory
location to tell the board
you have gotten it.

HTH,

Alan G. Smith


+---------------------------------------------------------
| Alan G. Smith
| .....agsKILLspamspam.....poboxes.com
| http://www.innovatus.com/ags

1997\09\28@231351 by Peter Wintulich

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The IRQ ack is software based. If you cannot find any examples then I can Get
you some.

You will need to write:  an ISR installer, The ISR its self and an ISR
uninstall. I have an example for MASM its 3 pages long! I might be able to fax
it ok

1997\09\28@231957 by Sean Breheny

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At 12:45 PM 9/29/97 +0930, you wrote:
>The IRQ ack is software based. If you cannot find any examples then I can Get
> you some.
>
>You will need to write:  an ISR installer, The ISR its self and an ISR
> uninstall. I have an example for MASM its 3 pages long! I might be able
to fax
> it ok
>

Thanks for the help. I think I know what you are talking about. I have
actually been writing IRQ handlers on the PC for a while, but I thought
that there might actually be an additional hardware ack. There is no need
to fax the example. Thanks again.

Sean


Sean Breheny,KA3YXM
Electrical Engineering Student

1997\09\29@215547 by jorgegf

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Hi

>
> Thank you for the information, but I still have one question, how does the
> microprocessor ack the IRQ? I am looking at a diagram of the ISA bus and I
> don't see any IRQ ack pin or anything like that.
>
> Thanks again,
> Sean
>
       The processor does ACK the Interrupt but this goes to the PIC
(Programmable Interrupt Controler) of the PC. The IRQ lines on the ISA
bus connect to the PICs and not directly to the processor. About the
duraction of the pulse I don't have exact numbers at hand, but I think
that the 5us that someone refered (as it hapens with the printer port)
are more than enought.


       best regards

       Jorge F

1997\09\30@200945 by Frans Gunawan

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At 11:34 PM 9/29/97 +0100, you wrote:
>Hi
>
>>
>> Thank you for the information, but I still have one question, how does the
>> microprocessor ack the IRQ? I am looking at a diagram of the ISA bus and I
>> don't see any IRQ ack pin or anything like that.
>>
>> Thanks again,
>> Sean
>>
>        The processor does ACK the Interrupt but this goes to the PIC
>(Programmable Interrupt Controler) of the PC. The IRQ lines on the ISA
>bus connect to the PICs and not directly to the processor. About the
>duraction of the pulse I don't have exact numbers at hand, but I think
>that the 5us that someone refered (as it hapens with the printer port)
>are more than enought.
>best regards
>        Jorge F

BTW, talking about 8259, you can look at my homepage about interfacing 8259
to 68hc11.
Sending ack is from software(IRQ handler).
goodluck.
http://www.poboxes.com/f
f

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