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'[PIC]: Question about interfacing modem to PIC'
2001\09\05@194518 by Eben Olson

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Sorry if this is a dumb question, but would it be at all possible to connect
a pic or sx microcontroller to an ISA or PCMIA modem? I'm trying to find a
way to send data from a robot to a computer, and I thought the cheapest way
would be to get an old modem and hook it up to a cordless phone, but I don't
know if the PIC has enough processing power to run a modem. Can anyone tell
me what this would involve, and if anyone's tried it before?

   TIA,
Eben Olson
P.S. Sorry about the double post, i forgot the : after [PIC]

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2001\09\05@210626 by Barry Gershenfeld

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>Sorry if this is a dumb question, but would it be at all possible to connect
>a pic or sx microcontroller to an ISA or PCMIA modem? I'm trying to find a
>way to send data from a robot to a computer, and I thought the cheapest way
>would be to get an old modem and hook it up to a cordless phone, but I don't
>know if the PIC has enough processing power to run a modem. Can anyone tell
>me what this would involve, and if anyone's tried it before?
>Eben Olson

Yes it's possible with ISA, I did it years ago with a Z80 (like a PIC in
a bigger package and 1/4 the speed :)   You can wire the ISA bus
connector up to look like most of the address for COM1 or 2 is
already selected.  Then you run a few of the port bits out to
there so you can select the remaining bits (which lets you select
the particular register).  I also ran one more bit that let
you select COM1 versus COM2 (3F8 vs. 2F8).  This gave me a
really neat option:  I could remove the modem and plug in
a 2-serial port card and I could talk to each port separately
under software control--attach an external modem on one port
and a serial terminal on the other and you have debug heaven.

To read and write to it takes data 8 bits and a strobe, just like
any parallel transfer.  Some PICs actually have a byte-wide
bus transfer mode on one of the ports you could use for this,
though I doubt it's all that necessary.

The rest is just a Small Matter Of Programming.

Er, I should have read your message more carefully, because it
looks like you want to put the cordless part of the phone
in the robot with the PIC and the modem.  I'm afraid the modem
is expecting to be connected to a phone line and getting a
wireless handset connected to it in place of that may turn
out to be the real challenge.

Barry

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2001\09\05@211232 by Brandon Fosdick

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Eben Olson wrote:
>
> Sorry if this is a dumb question, but would it be at all possible to connect
> a pic or sx microcontroller to an ISA or PCMIA modem? I'm trying to find a
> way to send data from a robot to a computer, and I thought the cheapest way
> would be to get an old modem and hook it up to a cordless phone, but I don't
> know if the PIC has enough processing power to run a modem. Can anyone tell
> me what this would involve, and if anyone's tried it before?

There have been several posts in the past about using small wireless
serial tranceivers for just this sort of thing. Try looking through the
archives.

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2001\09\06@115447 by Harold M Hallikainen

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On Wed, 5 Sep 2001 19:42:31 -0700 Eben Olson <spam_OUTbanielTakeThisOuTspamCROSSWINDS.NET>
writes:
> Sorry if this is a dumb question, but would it be at all possible to
> connect
> a pic or sx microcontroller to an ISA or PCMIA modem? I'm trying to
> find a
> way to send data from a robot to a computer, and I thought the
> cheapest way
> would be to get an old modem and hook it up to a cordless phone, but
> I don't
> know if the PIC has enough processing power to run a modem. Can
> anyone tell
> me what this would involve, and if anyone's tried it before?
>

       I believe it'd be pretty easy to connect an ISA modem to a PIC, though
it'd take a lot of pins (or some external shift registers or latches).
The ISA modem just looks like a serial port, so you have a few address
lines, 8 data lines, a read strobe, and a write strobe. Some of the
address lines can be hardwired to look like a standard com port address
so you don't have to use the PIC to drive them. Then, just send the modem
AT commands.
       The modem needs to be a whole modem, not a WinModem, which uses the host
to do signal processing. Doing host signal processing on a PIC would be a
pain!
       Also, I'd use a modem that has jumpers to set the address. I'd ignore
the interrupts and just poll it (possibly using a timer interrupt on the
PIC). Plug and play is probably pretty difficult to emulate on the PIC
(though I've never tried).
       Also, I think PCMCIA is pretty complicated when compared with ISA.
       Probably the simplest way to get a modem on a PIC is to use an external
serial modem and just drive it with the UART on the PIC. You'll need to
do TTL to EIA232 conversion, but that's not terrible. As far as I know,
external modems are always full modems, not WinModems.
       Good luck!

Harold



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