On Thu, 17 Feb 2000, Maciej W. Rozycki wrote:
> On Tue, 15 Feb 2000, Richard B. Johnson wrote:
>
> > Once programmed, there is no 'default vector'. The upper 5 bits of the
> > vector are set in ICW2. If there are no interrupt requests pending, there
> > are no vectors. Period.
>
> Go read the datasheet.
>
> > occurred is sufficient for the controller to 'remember' it for all time.
>
> Hmm, I guess you are writing of some other interrupt controller.
>
No he is referring to the 8259A.
> > It forgets it only when an EOI code is sent to the controller.
> > There are two, 0x20 is non-specific and 0x60|int_no is specific.
> > At this time, if the LTIM bit in the initialization register was not
> > set, the input latch is reset.
>
> You refer to ISR not to IRR, for sure. Go read the datasheets.
>
No. The in-service latch is what Johnson was refering to and, is
in fact, the memory of the chip.
> > The original 8259 was not designed for level-triggering, in fact
> > it was designed for use with 8085. It has a bit in ICW4 to select
>
> For 8080, actually.
>
No, the 8080 could not use vectored interrupts. The 8085 was correctly
shown.
> > the 8085 or the 8088 mode. The 'A' version and subsequent CMOS versions
> > provided a LTIM bit in the initialization register, ICW1 (bit 3). The
> > function of this bit is to prevent resetting the input latch when an EOI
> > (specific or non-specific) if sent to the device, IF the interrupt request
> > line is still true. This has the effect of allowing a level to be
> > detected. With this, multiple interrupt requests may be ORed into the same
> > IRQ line.
>
> You are writing of an INTA cycle for sure.
>
No. INTA comes from the CPU. Writing the EIO comes from the port, i.e.,
0x20 out port 0x20 by any means you want including the CPU.
> Please don't bother to comment on this mail -- there is no point in
> negating facts. Unless you are writing of something else than Intel
> 8259A. In this case please state clearly what IC you are writing of.
Sure, sure, sure. You call my collegue a liar and then hide in the
corner and cry. If you took the time to learn from your mistakes, you
might know something. Johnson spent some considerable time and effort,
reviewing his response with me, to show you how these very old devices
worked.
Very Truly Yours,
Charles Turner
Member(s) IEEE, IEEE Computer Society, AIAA
I speak only for myself, which is enough of a problem.
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