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PICList Thread
'3 (or4) serial ports'
1997\05\26@023731 by peter noble

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I have to confess that I am puzzled about all the talk about 4 serial
ports.

If you have a modem you get a fast port built in with that.  Most machines
come with two ports as standard.
My PIC programmer uses the parallel port.  My mouse uses Com1.  My modem
uses Com4.  I have no Com3 but that is no problem.  I have Com2 free for
any plug in serial devices (usually PIC based).

Why all the hassle about a 4th port I ask myself ????

TTFN  -  Peter.

1997\05\26@202327 by Gerhard Fiedler

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At 02:35 26/05/97 -0400, peter noble wrote:
>I have to confess that I am puzzled about all the talk about 4 serial
>ports.
>[...]
>Why all the hassle about a 4th port I ask myself ????

With a little fantasy it's easy to imagine 10 serial devices connected to a
single computer. I once did some work on a modem firmware and had four
(external, of course) modems connected at the same time to the same
computer. Or a couple of bar code readers or any other serial (RS232,
RS485) process devices... It's not all standard desktop apps what one might
do with a PC.


-------------------------------------
Gerhard Fiedler <spam_OUTgerhardTakeThisOuTspampobox.com>
S‹o Paulo - Brazil

1997\05\26@214505 by Mike Smith

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From: peter noble <.....elbonKILLspamspam@spam@COMPUSERVE.COM>
To: PICLISTspamKILLspamMITVMA.MIT.EDU
Subject: 3 (or4) serial ports
Date: Monday, 26 May 1997 16:05

>I have to confess that I am puzzled about all the talk about 4 serial
>ports.

>If you have a modem you get a fast port built in with that.  Most machines
>come with two ports as standard.

Some, maybe most of us, use external modems.  Not too much of a problem, as
simultaneous use of modem/development system isn't common.  A switch can
handle that...

>My PIC programmer uses the parallel port.  My mouse uses Com1.  My modem

A lot of PIC programmers use the serial port.  Again, the switch box can
hack this, as programming the hard code into a rom is relatively infrequent
( > 10min?)

Modern mouses (mice) can use the PS/2 port found on most motherboards, BTW.
Still uses an interrupt, though.

>uses Com4.  I have no Com3 but that is no problem.  I have Com2 free for
>any plug in serial devices (usually PIC based).

I thought it was supposed to be a bad idea to leave 'gaps' in your com port
map?

>Why all the hassle about a 4th port I ask myself ????

The hassle isn't getting 4 ports onto a systerm, I/O memory space isn't
*that* crowded.  Its the *&^% interrupts, and their scarcity!!  The cheap 4
port boards wont share ints between ports, and as for sharing off-board -
forget it!  A solution would be a PCI based multifunction board , as the
ints on them can be level, rather than edge triggered.

Why would you want so many ports active?  Consider this scenario.  You have
an emulator on one port, the rs232 of the device being emu'ed on another,
the rs232 of another device which 'talks' to the emu'ed device, but has a
windowed chip in it.  That's 3 ports, and they *have* to be simultaneous.
If you're writing a PC level program to communicate down the rs232, it
becomes even trickier, as you can't even use a dumb (XT say) terminal - you
need something that can run Win95.  This might seem involved, but its one
of a few scenario's I'm using that need > 2 ports.

On this subject, anyone know where in Oz I can get the boards that are
being discussed here?

MikeS
<.....mikesmith_ozKILLspamspam.....relaymail.net>

1997\05\27@122739 by Harold Hallikainen

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       Back at work now, I can look up the multiport board info.  First
off, Boca Research (+1 407 241 8088) makes a series of multiport boards.
These include the

       BB1004  4 port board
       BB1008  8 port board
       BB2016  16 port board

       Each port is similar to 1 16550 and takes 8 bytes of I/O space.
All ports drive one interrupt line and a status byte is available with
flags from all ports.

       The other board I've used is the GTek PCSS-8I.  GTek can be
reached at +1 601 467 8048.  This board includes its own processor,
firmware and RAM.  It dynamically allocates buffer space in RAM to the
ports, as needed.  The standard board comes with 32 K RAM.  The board
uses 4 registers in I/O space.  A large number of commands are used to
send and receive data, select which port to use, etc.  In many
applications interrupts are not required, since the board buffers the
data for you.  Just poll the board.  The board does support interrupts.

       Each of these boards also come with drivers to support a variety
of operating systems.


Harold

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