[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: Hay you hardware hackers ...
Ok, here it comes from the hardware guy, the hardware facts:
There are 2 kinds of COM ports, 100% compatible and the other kind.
The other kind, is what you get when you have a chipset that emulates a
serial chip for Winblows and Winblows only, in a laptop machine, or in a
Plug & Pray modem of newer generation. These are made for, and work with
their drivers *ONLY*.
The 100% compatible kind, is hardware compatible with the NS (National
Semiconductor) 16540, 16550 or 16550A chips. By hardware compatible, I
mean register level compatible. The data sheets of these chips are
available as PDF documents from the website of the quoted party.
A 100% compatible port built with these chips, or with something that
emulates them well (such as a Cyclades board for example), looks exactly,
precisely and indistinguishably like a 16550 chip from register side.
The 'disabling' of serial ports is done in 2 ways:
The BIOS can disable ports that are embedded in the chipset, by turning
off some gates in the ASICs. When these gates are turned off, then they
are off, and I mean *off*. Unless you (or Linux) knows how to turn them
back on, they stay so.
Linux has got support for some chipsets and it is possible that it turns
on the serial ports that were turned offby the BIOS, if that support comes
into play, at boot time. This means, that it sets the mentioned registers
(knowing where they are).
Turning on a serial port, and tunring on its interrupt are 2 different
things. The interrupt is turned on by setting the bit called OUT2 to 1 in
a certain register of the 16550 chips. This does not determine to which
IRQ it gets mapped. The IRQ is determined by jumpers, or by the BIOS
preset (one of 2 values usually). It is possible to use a serial port, at
low speed, in polled mode, without interrupts, assuming that the hardware
handshake lines are used correctly.
Eddie, it would be extremely helpfull, if you would tell us what kind of
serial port that is, and what chipset, and what BIOS (whose) (CPU does not
matter).
On Mon, 5 Jan 1998, Eddie Harari wrote:
> >
> >On Sun, 4 Jan 1998 17:13:47 +0200 (IST), you wrote:
> >
> >>hello to all of the hardware hackers over this list ,
> >>
> >> I have a Pentium-200MHZ with 2 serialport on board ,
> >> now I installed a modem as Com one IRQ-4 which is a different
> >> card on the board ...
> >>
> >> the problem is that The only way I can cancel the on board com port=20
> >> is thry the cmos menues ...=20
> >>
> >> and I know linux does not consult these menus ...
> >> so when I try to use minicom with cua0 or seyon I canot activate=20
> >> the modem ...
> >This is not true! The CMOS menus does not do a "software" action. They
> >actually DISABLE the onboard port. Linux is not supposed to mess with
> >this. Disabling COM1: through the BIOS should work. COM1: is IO 0x3f8
> >and IRQ4. Make sure no port is assigned to that address, other than
> >your modem.
>
> Well I know what you say , and I cant say I disagree with you ,
> but when I disable com I thru my cmos Linux still recognize it !!!
>
> >
> >> cause it is trying to talk to com port I and not to my modem ...
> >>
> >> the only way I activate my modem is by disabling its PNP and set=20
> >> the modem up as com port 3 then everything is OK ...
> >>
> >> But is this the way ???
> >
> >Udi
> >
>
>
> --
> Eddie Harari - phone: 972-3-6190999
> fax : 972-3-6190992
> ___________________
> Take A Walk In The Wild Side ...
>
>
>
>
>