Very Computer

i have a question.. is there any way the parallel port can output more than
1 byte of data simultaneously? or just those 8 bits? I don't know a great
deal about the PC's hardware system, but I'd like to 'enhance' the meter for
my pc... :) Thanks!

I've thought about getting a LCD display or something with a builtin
chipset to display more complex stuff, but i really can't afford one...

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   i have a question.. is there any way the parallel port can output more than
   1 byte of data simultaneously? or just those 8 bits? I don't know a great
   deal about the PC's hardware system, but I'd like to 'enhance' the meter for
   my pc... :) Thanks!

   I've thought about getting a LCD display or something with a builtin
   chipset to display more complex stuff, but i really can't afford one...

First part:  Yes, you can demux the port .. it only takes a few IC's.
You don't really need to have all of the bits on at the same time,
though, since this is just a display.  You can do what is done in
industry a lot in alarm clocks, etc, and that is to multiplex the
segments.  For instance, you could use one output bit, and 4 address
bits, and if you write a sufficiently fast routine, you can give the
illusion of having 16 LEDs lit or unlit.. You just flip through each
address, setting the output bit accordingly, very quickly.  This is a
trivial task, both in hardware and software.  Actually, now that I
think of it, you could do it with some latches, too.. Which'd reduce
the needs on the software end..

Secondly.. If you want an LCD like I have, a non-backlit 40x2 display
runs about $13 .. My backlit 40x2 cost $25.  I'll give you the device
driver code I wrote, if you want it.

Either way, it's easy to do.

Steve.
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:    i have a question.. is there any way the parallel port can output more than
:    1 byte of data simultaneously? or just those 8 bits? I don't know a great
:    deal about the PC's hardware system, but I'd like to 'enhance' the meter for
:    my pc... :) Thanks!

:    I've thought about getting a LCD display or something with a builtin
:    chipset to display more complex stuff, but i really can't afford one...

: Secondly.. If you want an LCD like I have, a non-backlit 40x2 display
: runs about $13 .. My backlit 40x2 cost $25.  I'll give you the device
: driver code I wrote, if you want it.

: Either way, it's easy to do.

  I'd be interested in seein gyour device driver code. I have a daemon
that runs in the background displaying the loadaverage, date/time and
memory usage on a 16x2 LCD hooked to the parallel port.

    Brian

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: You can't output more than one byte simultameously on a parallel port.
: However, it wouldn't be too diffucult to create a demuxing circuit with
: two latch chips and a flip-flop.  I'm not sure exactly how it would be
: wired off-hand, but basically STROBE toggles the flip-flop to determine
: which latch receives the next byte from the computer.  If you want to
: get fancy, you can use the RESET line to resyncronize by having it set
: or reset the flip-flop.  All the software has to do then is output the
: two bytes.  Byte order is basically determined by how you set you
: latches to receive.  Effectivly, you have 16 bits to do with as you
: please.

  I would think that using, say 2 or three bits of the output byte
as an address would work great.  Use, say bits 0 and 1 as an address
decode, and route the other 6 bits to the latches.. You'd only be
using 6 of the bits of each latch, but you'd get an effective of
24 bits and you wouldn't have to worry about the flip-flop sync
and all that stuff with the reset line..

        Of course if you REALLY wanted to get fancy, you could combine
both of these ideas and use the flip-flop thing to select the first
byte as the address, and the second byte as the data..
        But what in TARNATIONS would one do with 2048 leds..  :)

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        Mark Smith
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This is not true.  There are also status lines that you can use.  I can't
recall offhand how many.

: However, it wouldn't be too diffucult to create a demuxing circuit with
: two latch chips and a flip-flop.  I'm not sure exactly how it would be
: wired off-hand, but basically STROBE toggles the flip-flop to determine
: which latch receives the next byte from the computer.  If you want to
: get fancy, you can use the RESET line to resyncronize by having it set
: or reset the flip-flop.  All the software has to do then is output the
: two bytes.  Byte order is basically determined by how you set you
: latches to receive.  Effectivly, you have 16 bits to do with as you
: please.

: Larger frames could be supported by adding more latches and control
: circuitry.

This _is_ true, and would work, if you have the experience required.

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You can't output more than one byte simultameously on a parallel port.
However, it wouldn't be too diffucult to create a demuxing circuit with
two latch chips and a flip-flop.  I'm not sure exactly how it would be
wired off-hand, but basically STROBE toggles the flip-flop to determine
which latch receives the next byte from the computer.  If you want to
get fancy, you can use the RESET line to resyncronize by having it set
or reset the flip-flop.  All the software has to do then is output the
two bytes.  Byte order is basically determined by how you set you
latches to receive.  Effectivly, you have 16 bits to do with as you
please.

Larger frames could be supported by adding more latches and control
circuitry.

        --Andy

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Holger

I've built a box that's something like that (with 3 74HC373s), and the
only problem I ran into was ringing and crosstalk on the parallel port
lines.  This is pretty easy to solve with 1k Ohm/.01uF low-pass filters
on the clock lines.  The data lines tend to take care of themselves after
you cool off the handshake lines.  You could probably get away with a
smaller cap if you want some speed (15kHz max for the above values).

Randy Smith

Connect the three lines to Adress-Input's of an 74#138, and the Strobe
to one Enable of the '138. You'll be able to control 8 different 8-Bit
Latches without too much hassle.

Quote:>    Mark Smith