29 Dec
2005
29 Dec
'05
4:41 a.m.
2. (might as well ask, as long as I'm asking) I
know you dislike
the whole "board swap" mentality and that you prefer replacing
blown chips over replacing a whole board. But why not repair those
non-functioning chips? I mean, one blown gate and you toss the
I am not sure anyone can repair a chip. Are you suggesting I start moving
atoms around to correct the wrong doping levels, oxided metal traces, etc? The 7400 chip is documented to work under certain
conditions, with these
inputs and output. Just as a two port serial card for the PC is documented
to work with the ports at such-n-such address with so-n-so IRQ and what not
(or else, not many people will buy the thing).
And there your analogy breaks down. I have the Texas Instruments data
sheet foe the 7400. It's several pages long (I can go and get it if you
like), it includes a component-level schematic of that NAND gate, it
contains a lot of electrical specifications. And that's for a very simple
chip.
If a Texas Instruments SN7400 fails, I can use those specs to work out
that I don't _have_ to get the exact same part most of the time. Many
other comapanies made chips with similar, if not indentical, specs. There
wrre other families of TTL logic -- say 74S00,74LS00, etc that have
different specs, also documented. Again, in some applications I can use
those, in some I can't. The specs let me be sure.
I might be happier treating a board -- a motherboard or an I/O card -- as
a component if I could get proper documetation and specs for it. When was
the last time you saw a motherboard that came with pinout and timing
diagrams? With a bit-level description of every I/O register used on that
board? and so on. Without that information, if my motherboard fails and
that particular one is no longer in production, how do I know that the
one I replace it with is going to behave in the same way under all
conditions.
I keep on seeing PC-related products that come with drivers for the
current version of Windows, but nothing else, and no available
specifications to write drivers for other OSes. That's like supplying a
chip withot a data sheet, just a sort-of applications circuit. Totally
useless if you actually want to do something different with the product.
And to return to the PC serial port card. Can you please tell me where to
find a clone serial card that is exactly compatible in all respects with
the IBM one in my PC/XT system [1]?
[1] Note for the uninitiated. The IBM serial card has 2 odd features that
were not present in most, if not all, clones. The first is that it can
pull pin B8 (IIRS) low during I/O reads, needed if the card is used in
slot 8 of the IBM PC/XT. The second is that it has a current loop
interface as well as RS232 .
Maybe to you,
but it's not happened here yet.
"Here" being your house? Or England? Because it's certainly a reality