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PICList Thread
'MUX'
1998\02\13@145500 by H.P.d.Vries

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Does anyone know of a Bidirectional 32-8 multiplexer? (or 16-4, 4-1)

I want to multiplex an 8-bit I/O port of a PIC to 4 sources/destinations
of/for the data. I hope somone understands this ....

Hans

1998\02\13@153814 by Nicholas Irias

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One possible solution is to use tri-state 8-bit bus transceivers at
each of the 4 destinations or sources.  You can use 4-bit magnitude
comparators at each destination to compare a bus address to the
destination address, and use the address==address to enable the
transceiver.  This supports 16 addresses.

This requires a bus with 8 data lines, 4 address lines, and one flow
control line, to control the data direction of the selected transceiver.

This method is definitely bulkier and less elegant than a 2 wire
I2C bus, but your software winds up being incredibly simple, at
least if each slave device is either always an input or always an
output.  The software in a slave device is just reading or writing to
its 8 pins, and can be oblivious to the outside world.  No need to
perform some communication task every few uSecs.

The relevant parts are DM74LS85 and DM74LS245.  Note that you
will need to invert the A==B output from the magnitude comparator
before feeding it into the transceiver.


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{Quote hidden}

1998\02\13@155909 by H.P.d.Vries

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This way I have a few bits too few. I am using a PIC16C84, which has a
total of 13 I/O bits. But if I use only 3 address-bits, and preset the
ttransceivers for either input or output this should worh (I hope)

Hans

Nicholas Irias wrote:
{Quote hidden}

1998\02\13@165832 by Nicholas Irias

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I should have mentioned, for devices which are always outputs
you might want to use an 8-bit latch, like the DM74LS573, instead
of the bus transceiver.  When the addresses match, use the
comparator's output to set the latch enable high, storing the value.
That way, the slave PIC doesnt need to poll the input pins.  It just
reads the latch whenever it gets around to it.

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{Quote hidden}

1998\02\14@112220 by Leon Heller

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In message <@spam@34E51D68.5CDCKILLspamspamstud.tue.nl>, "H.P. de Vries"
<KILLspamH.P.d.VriesKILLspamspamSTUD.TUE.NL> writes
>Does anyone know of a Bidirectional 32-8 multiplexer? (or 16-4, 4-1)
>
>I want to multiplex an 8-bit I/O port of a PIC to 4 sources/destinations
>of/for the data. I hope somone understands this ....

If you can't find something off-the-shelf, and you need a single-chip
solution, a CPLD like the smaller Lattice isp parts is ideal for this
sort of thing. Lattice provides development software on their free CD-
ROM, and all you need to program the parts in-circuit is a download
cable connected to the printer port - they provide the schematic, or you
can buy it. The Lattice URL is:

       http://www.lattice-semi.com

Leon
--
Leon Heller: RemoveMEleonTakeThisOuTspamlfheller.demon.co.uk http://www.lfheller.demon.co.uk
Amateur Radio Callsign G1HSM    Tel: +44 (0) 118 947 1424
See http://www.lfheller.demon.co.uk/dds.htm for details of my AD9850
DDS system. See " "/diy_dsp.htm for a simple DIY DSP ADSP-2104 system.

1998\02\16@080808 by Claudio Rachiele IW0DZG

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 I think that in embedded control I/O pins are never enought.
Why don't  you try to use 4x4094 in cascade ? only 3 pins used to 32 bits out
!!!!!!
For input  you can use 4014 in same way. Istead  of 4x4094 you can use only one
MM5450.
TRY to THINK SERIAL.
ciao.

                      Claudio Rachiele IW0DZG

1998\02\16@102942 by Nuno Filipe Pedrosa

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> TRY to THINK SERIAL.

 Howa!
 This interests me. How can I find out more about these chips? I needed
a simple way to increase my I/O pins count.
 Any more ideas or chips on how to do that?

 Thanx,
 Nuno.

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1998\02\16@123149 by Jon Hylands

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On Mon, 16 Feb 1998 15:12:37 +0100, Nuno Filipe Pedrosa
<TakeThisOuTnffpEraseMEspamspam_OUTDIONE.IST.UTL.PT> wrote:

> > TRY to THINK SERIAL.
>
>   Howa!
>   This interests me. How can I find out more about these chips? I needed
> a simple way to increase my I/O pins count.
>   Any more ideas or chips on how to do that?

Yeah, check out the Philips I2C I/O expander. If you already have an
I2C bus in your system, it costs nothing in terms of pins on your uC,
and you get 8 pins of extra I/O. Since you can add up to eight of
these chips on an I2C bus, you can get up to 64 extra I/O pins.

The part number is PCF8574. It's a 16 pin DIP, or a 2- pin surface
mount.

Peter Anderson has a good article interfacing to it on his PIC page
(including the low-level I2C driver for an 16C84), check out
http://www.access.digex.net/~pha/PIC/16C84/8574_1.html.

The data sheet for it can be found on the Philips Semiconductor page
at http://207.87.19.21/acrobat/datasheets/PCF8574_2.pdf.

Later,
Jon

--------------------------------------------------------------
  Jon Hylands      RemoveMEJonspamTakeThisOuThuv.com      http://www.huv.com/jon

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1998\02\17@045527 by Claudio Rachiele IW0DZG

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On - CHIP DIRECTORY - site you can find everything . Dontronics and Scott
Edwards sell a ready made i/o expander, but 4094, 4014, MM5450 and MM5480 are
less expensive.
Pay attention to 4014 use it JAM inputs and register contents. You must clean
register before
load it with inputs.

                      Claudio Rachiele IW0DZG

1998\02\17@164307 by paulb

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Jon Hylands wrote:

> On Mon, 16 Feb 1998 15:12:37 +0100, Nuno Filipe Pedrosa
> <nffpEraseMEspam.....DIONE.IST.UTL.PT> wrote:
>
>>> TRY to THINK SERIAL.
>>
>>  Howa!
>>  This interests me. How can I find out more about these chips? I
>> needed a simple way to increase my I/O pins count.
>>  Any more ideas or chips on how to do that?

> Yeah, check out the Philips I2C I/O expander. If you already have an
> I2C bus in your system, it costs nothing in terms of pins on your uC,

 All very well and good.  If however, you wish to use three pins, two
of which can be used for some other tasks as well, here is my favourite
source for logic data sheets:
       http://www.st.com/stonline/books/pdf/menu/06040100.htm

 Note these are HCMOS rather than CMOS.  Restricted to 5V, but faster
*and*, most important, higher drive capabilities although not quite as
powerful as the PIC itself.

 Cheers,
       Paul B.

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