Talk:Intel 8259

Kudos & Correction

Just wanted to say "good work" to the editors of this page! I had to debug an interrupt problem and this page gave me the information I needed without having to read the detailed datasheets. Thanks! — Preceding unsigned comment added by 70.239.231.49 (talk) 21:10, 25 April 2007 (UTC)

(Note: The above is not from me, but the original author forgot to "sign" his post!) The article tells:

"The 8259 was included in the original PC introduced in 1980 and maintained by the PC/XT when introduced in 1983."

This is not true. In fact, it cannot. The original 8259 was only able to interface the 8080 and 8085. It was the 8259A that introduced the ability to be configured to interface the 8086. Source: Any intel datasheet an the 8259A, for example from http://bochs.sourceforge.net/techspec/intel-8259a-pic.pdf.gz. It states on the first page: "The 8259A is fully upward compatible with the Intel 8259. Software originally written for the 8259 will operate the 8259A in all 8259 equivalent modes (MCS-80/85, Non-Buffered, Edge Triggered)." (Note that MCS-80 is a synonym for the 8080, MCS-85 a synonym for the 8085).

Spiro Trikaliotis 13:56, 3 November 2007 (UTC)

The entire page could use some editing. As the above comment says, no PC ever used an Intel 8259 if Intel's 8259A datasheet is to be believed; it had to be an 8259A. (And wasn't the original PC introduced in 1981 anyway?)

Further, many people appear to be confused about the difference between the IBM PC and XT. Wikipedia uses 'PC/XT' to designate the XT, which is in line with using 'PC/AT' as a shorthand for the Personal Computer AT. But then the section on edge/level triggered interrupts seems to talk only about the XT and AT and not about the original PC.

Some explicit mentions of 'x86' probably ought to be removed when talking about general use of the 8259(A). Clearly the PIC also works with Intel's 8080/8085 chips, if not in other systems with non-Intel CPUs. Or perhaps it should be made clearer when the article is talking about actual 8259A and when it's talking about work-alikes used in PC compatibles.

MichalN (talk) 11:31, 22 November 2007 (UTC)

(this was ignored for the design of the PC for some reason)

An interesting statement, and I'm not sure it has its place in this page. The iAPX86/88 Users Manual (1981 Edn; C-258/781/45K/RRD, and a bit dogeared now) states:

"As show in figure 4-18, the first five interrupt vectors are associates with the software-initiated interrupts and the hardware non-maskable interrupts (NMI). The next 27 interrupt vectors are reserved by Intel and should not be used if compatibility with future Intel products is to be maintained".

Presumably the IBM hackers (it was a stink-works project after all) thought that leaving 3 free was plenty... I'll cross reference the PC page. Number774 (talk) 19:22, 15 April 2019 (UTC)