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'[EE]: PC Parallel Port -- Issues and Inquiry'
2001\07\31@212044 by Wade Carpenter

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Hello,

-- Warning --
-- Stupid question following below =)

Looking for someone with good knowledge of the PC's parallel port, new and
old computers.

I am trying to interface to the parallel port, and I am having no luck -
absolutely none.

Here is what I am starting with for knowledge (assumptions?):

1) Outputs are open collector type.
2) Pin configuration of the port.

Now some places (I.e. a certain parallel port FAQ at
http://www.lvr.com/files/ibmlpt.txt) will tell me that the outputs are TTL.

Here's where I noticed that I'm not able to get it to work properly.  I
tried to connect the port to a 74LS05 (Inverter) and the output and inputs
to this chip are something like 1.3V. Total garbage.  Regardless of the
port's state.  I do believe that the software I'm using to toggle all of the
outputs on the port is correct.

Any ideas???

Thanks,

Wade

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2001\07\31@214152 by David Venz

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Hmmm.....

Some quick things (you may have already tried):
1) See if you get the same "garbage" results without the '05 attached (i.e. look
directly at your parallel port pins)
2) Tie all unused '05 input pins to GND or VCC (comments?)
3) Use pullups of ~10k on '05 outputs?
4) Check that the parallel port cable that you're using brings all the signals
you want thru, without crossing any over either.  I.e. D0->D0, ACK->ACK etc.

-Dave.

Wade Carpenter wrote:

{Quote hidden}

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2001\07\31@215012 by Greg Doyle

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For starters try:

http://www.2xtreme.net/dage/parport.html



includes enough to get you into trouble and even a cute little led tester
and qbasic prg.

Greg




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2001\07\31@221813 by Patrick J

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Hi, I am in the finishing stage of the first part of a project there a PIC16F877
is used to interface the parallell port. I am sending and reciving address and
data bytes via the parallell port in EPP v1.9 mode at 150 KB/S.
Note: Old parallell ports cant do EPP/ECP, just SPP (standard mode)

Unfortenatly I havent done the schematic yet, but this is what I use in short
for EPP bidirectional mode:
8 databits PIC <- inline resistor 470ohm -> P.port
3 handshake signals PIC <- inline resistor 1000ohm -> P.port
1 handshake signal OC PIC <- pullup 10k & inline resistor 1000ohm -> P.port

I dont know in which mode you are using the port but a few gotcha for EPP are
- u must ACK in less than 10uS
- watch out for the small difference between v1.7 and v1.9
- check and reset (if needed) the timeout flag
- init the port correctly

Also check out this site http://www.beyondlogic.org

/PJ

----- Original Message -----
From: "Wade Carpenter"
> I am trying to interface to the parallel port, and I am having no luck -
> absolutely none.
> 1) Outputs are open collector type.
> 2) Pin configuration of the port.

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'[EE]: PC Parallel Port -- Issues and Inquiry'
2001\08\01@064927 by Vasile Surducan
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I like this one:
http://www.beyondlogic.org/index.html#PARALLEL
Vasile

On Tue, 31 Jul 2001, Wade Carpenter wrote:

{Quote hidden}

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2001\08\01@070035 by Darren Twiss

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Hi Wade,

I have done a project that sounds very similar to what you are doing. I used
EPP to a 16F877. Connected via a FIFO.

There are a lot of traps to fall into. To make it worse a lot of literature
I found was misleading.

firstly I found that the EPP port doesn't like TTL so I would try the CMOS
equivalent of the inverter.

Looks like people have given you the best links so I won't repeat them.

What platform is your host running on and what sort of data transfer are you
doing?

One thing I wish I had done earlier in my project is find out more about the
particular EPP port I was using (eg chipset,mode). This can catch you out.

Good luck, keep us posted

Darren

Darren Twiss
B.Sc.
Electronics Engineer
Hamilton
New Zealand


{Original Message removed}

2001\08\01@072847 by Vasile Surducan

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On Wed, 1 Aug 2001, Darren Twiss wrote:

> Hi Wade,
>
> I have done a project that sounds very similar to what you are doing. I used
> EPP to a 16F877. Connected via a FIFO.
>
 Interesting ! And what was the biggest transfer rate you've got ?

Vasile

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2001\08\01@084637 by Olin Lathrop

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> Here's where I noticed that I'm not able to get it to work properly.  I
> tried to connect the port to a 74LS05 (Inverter) and the output and inputs
> to this chip are something like 1.3V. Total garbage.  Regardless of the
> port's state.  I do believe that the software I'm using to toggle all of
the
> outputs on the port is correct.

Something is definitely wrong electrically if the *outputs* of the 74LS04
are also around 1.3V.  Check the power to the chip.  What are the port
output levels with nothing connected?  Is the LS04 oscillating?  You say
your software to drive the port is working (although I don't know how you
can tell given what you told us), so toggle all the bits in some pattern and
look at the bare outputs with nothing connected.  If that looks fine,
incrementally add more stuff and keep following the signals to see where
they get lost.

I like to use a counting pattern for this sort of thing.  Each bit is a
square wave with half the frequency of the next lower bit.  This makes it
easy to identify bits and detect shorts between them.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, spam_OUTolinTakeThisOuTspamembedinc.com, http://www.embedinc.com

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2001\08\01@094353 by Wade Carpenter

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Thanks to everyone fo the great response, it's much appreciated!!

Darren - The host is a Win98 machine, and I'm just trying to use it
eventually for programming PIC's.  The problem is, I started building up one
of these interface circuits, and the outputs I keep getting are not what I'd
expected.  But I am just using a voltmeter to check this.  I don't have a
scope at home.

Olin - By the sound of your message, it seems that I am way off base here,
and that I won't be able to check this out without using a scope.  So the
outputs of the parallel port are not a constant high or low then?  I haven't
had a chance to read any of the links yet, nor try to implement any of the
suggestions.

Thanks,

Wade


{Original Message removed}

2001\08\01@103751 by Roman Black

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Wade Carpenter wrote:

> > > Here's where I noticed that I'm not able to get it to work properly.  I
> > > tried to connect the port to a 74LS05 (Inverter) and the output and
> inputs
> > > to this chip are something like 1.3V. Total garbage.  Regardless of the
> > > port's state.  I do believe that the software I'm using to toggle all of
> > the
> > > outputs on the port is correct.


Hi Wade, I often use the parallel port
for quick and nasty PC interfacing. :o)

Have you connected the 0v (gnd) of your
logic chip to the main ground pins in the par
port? Did you connect all the ground pins
in the par port together? Make sure you do
both of these.

The par port should be outputting standard
type logic levels, about 0.6v for low and
3.5v to 4.2v for high.

If you connect to the INPUTS in the par port,
these normally have a fairly strong pullup
resistor attached and you will need a very
low series resistor, any values over 180 ohms
will fail to pull the par port inputs low
enough, 120 ohms is a good value.

For the par port OUTPUTS just use a 1k or 2k2
resistor between the par port output and your
logic chip input.

Also check your PC bios settings, even old
286/386 usually have EPP capability, just they
are normally set to "standard" in the bios.

Hope that helps. Maybe you should show your
circuit??
:o)
-Roman

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2001\08\01@165511 by Olin Lathrop

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> Olin - By the sound of your message, it seems that I am way off base here,
> and that I won't be able to check this out without using a scope.

A scope would definitely be useful.  I was assuming you were using one.

> So the
> outputs of the parallel port are not a constant high or low then?

I was suggesting you program them with a counting pattern and look at the
output on a scope to see where the signal is getting lost.


********************************************************************
Olin Lathrop, embedded systems consultant in Littleton Massachusetts
(978) 742-9014, .....olinKILLspamspam@spam@embedinc.com, http://www.embedinc.com

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2001\08\01@210258 by Patrick J

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From: "Roman Black"
> If you connect to the INPUTS in the par port,
> these normally have a fairly strong pullup
> resistor attached and you will need a very
> low series resistor, any values over 180 ohms
> will fail to pull the par port inputs low
> enough, 120 ohms is a good value.
>
> For the par port OUTPUTS just use a 1k or 2k2
> resistor between the par port output and your
> logic chip input.

I had 1k resistors between the port and the pic and got
random data. After changing to 470 ohms i got a reliable
data transmission. Maybe you need 470 to be able to
drive the cap. in some ports.
The strange thing was that that i could SEND reliable,
but when reciving data on the PC it was random.

Now my test program has sent more than 10 mil data bytes
and zero error bytes in return. And no timeouts.

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2001\08\02@022401 by Darren Twiss

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Wade -

I have had problems with Win98 and the p.port. Basically I send data from
the PC to the PIC. However sometimes the data doesn't get through. I have
spent quite a lot of time looking at this and have come to the conclusion
that Win98 is the problem.

My theory is that my peripheral does not implement some of the features that
win98 and its deveice drivers require. I have come accross some literature
that talks about windows querying the deveice on the lpt port and the device
is supposed to send back data ( about its mode and plug'n'play config). My
device does not do this and I think that it is because win98 keeps asking
every now and then 'who are you and what are you doing hanging off my lpt
port'.

My logic behind this is that if I read my data register after each transfer
( so it should contain the data I just sent) a lot of the time this is not
the case. I can send my data to the pic, the data is received because my
device works, but by the time I read the data register it has something else
in it. I can also see extra data strobes present during transmission.

I am putting this down to win98, I could probably fix it by way of writing a
virtual device driver but that is not an option right now.

Anyway, pure MS-DOS is a great OS...

If anyone else has any ideas..................on my problem.....thanks


{Original Message removed}

2001\08\02@061818 by Roman Black

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Patrick J wrote:
{Quote hidden}

Patrick, it's exactly what I mentioned above,
when receiving data on the PC you need to pull down
the logic level against the pull-up resistors in the
PC par port. Use 120 ohm resistors!! It may work now
with 470 ohms, but when moved to other PCs you will
get problems. Trust me! :o)
-Roman

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