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Decoding 2 bit to 4 — Parallax Forums

Decoding 2 bit to 4

ArchiverArchiver Posts: 46,084
edited 2000-08-07 15:26 in General Discussion
Does anyone know of an IC that EXACTLY matches this truth table:

IN OUT
| a b | 1 2 3 4 |
|
|
|
| 0 0 | 1 0 0 0 |
| 0 1 | 0 1 0 0 |
| 1 0 | 0 0 1 0 |
| 1 1 | 0 0 0 1 |

The 74x195 & 74x155 have the outputs reversed from this, and I would have to
use a set of inverters, and i REALLY needed to keep the # of devices to a
minimum. So, if anyone knows of a device...


Thanks in advance,
Edward Kindler

Comments

  • ArchiverArchiver Posts: 46,084
    edited 2000-08-07 01:43
    There are many:
    CD4028 is straightforward.
    CD4514 can do this using q8 q9 q10 q11 as outputs and setting A3 High.
    The CD4051 8ch analog multiplex is OK (must use pull up /or down
    resistors ? ).

    ACJacques


    RiffRaff82@a... wrote:
    >
    > Does anyone know of an IC that EXACTLY matches this truth table:
    >
    > IN OUT
    > | a b | 1 2 3 4 |
    > |
    |
    |
    > | 0 0 | 1 0 0 0 |
    > | 0 1 | 0 1 0 0 |
    > | 1 0 | 0 0 1 0 |
    > | 1 1 | 0 0 0 1 |
    >
    > The 74x195 & 74x155 have the outputs reversed from this, and I would have to
    > use a set of inverters, and i REALLY needed to keep the # of devices to a
    > minimum. So, if anyone knows of a device...
    >
    > Thanks in advance,
    > Edward Kindler
  • ArchiverArchiver Posts: 46,084
    edited 2000-08-07 02:26
    What you want is a 74X239 (where X is HC, L, F, whatever you need to match
    the rest of your circuit). If you can't find one, try a 74X238 and ground
    the extra input (and ignore the extra outputs).

    Regards,

    Al Williams
    AWC
    * Floating point math for the Stamp, PIC, SX, or any microcontroller at
    http://www.al-williams.com/awce/pak1.htm

    >
    Original Message
    > From: RiffRaff82@a... [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=jvWyjfxKGI1Pq3_J7utIE8kGdEQeGu9C2CL8JHa1YFV9D9ujp2QGUtJryOytUZJlUxFz1LiGirw]RiffRaff82@a...[/url
    > Sent: Sunday, August 06, 2000 6:51 PM
    > To: SeattleRobotics@egroups.com; basicstamps@egroups.com
    > Subject: [noparse][[/noparse]basicstamps] Decoding 2 bit to 4
    >
    >
    > Does anyone know of an IC that EXACTLY matches this truth table:
    >
    > IN OUT
    > | a b | 1 2 3 4 |
    > |
    |
    |
    > | 0 0 | 1 0 0 0 |
    > | 0 1 | 0 1 0 0 |
    > | 1 0 | 0 0 1 0 |
    > | 1 1 | 0 0 0 1 |
    >
    > The 74x195 & 74x155 have the outputs reversed from this, and I
    > would have to
    > use a set of inverters, and i REALLY needed to keep the # of devices to a
    > minimum. So, if anyone knows of a device...
    >
    >
    > Thanks in advance,
    > Edward Kindler
    >
    >
  • ArchiverArchiver Posts: 46,084
    edited 2000-08-07 06:06
    At 07:51 PM 8/6/00, you wrote:
    >Does anyone know of an IC that EXACTLY matches this truth table:
    >
    > IN OUT
    >| a b | 1 2 3 4 |
    >|
    |
    |
    >| 0 0 | 1 0 0 0 |
    >| 0 1 | 0 1 0 0 |
    >| 1 0 | 0 0 1 0 |
    >| 1 1 | 0 0 0 1 |
    >
    >The 74x195 & 74x155 have the outputs reversed from this, and I would have to
    >use a set of inverters, and i REALLY needed to keep the # of devices to a
    >minimum. So, if anyone knows of a device...

    Either of the following decoders will ehibit the outputs you desire:

    CD4028 National HEF4028 Philips

    Both are BCD to Decimal, or Binary to Octal - Decoders. Both are a bit of
    overkill, as they are wider than necessary, but so it is with 4-bit
    requirements.
    The National part has 4 input buffers and 10 output buffers (2/4, 3/8,
    4/10). Not sure about the Philips unit.



    >Thanks in advance,
    >Edward Kindler

    Surely

    Regards,

    Bruce Bates
  • ArchiverArchiver Posts: 46,084
    edited 2000-08-07 06:25
    At 08:26 PM 8/6/00, you wrote:
    >What you want is a 74X239 (where X is HC, L, F, whatever you need to match
    >the rest of your circuit). If you can't find one, try a 74X238 and ground
    >the extra input (and ignore the extra outputs)


    Just for the record, the CD74xx238 is available from TI, and the 239 is
    obso and only available from Rochester.

    Regards,

    Bruce Bates

    >.
    >
    >Regards,
    >
    >Al Williams
    >AWC
    >* Floating point math for the Stamp, PIC, SX, or any microcontroller at
    >http://www.al-williams.com/awce/pak1.htm
    >
    > >
    Original Message
    > > From: RiffRaff82@a... [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=yrizUp65W6MeiQaxXi36OeyxpR8sfzpmi9IVgYhyPn6EvuPzcNo2fPDftzV88IVaEtwgnnV6vGt5aFhdJw]RiffRaff82@a...[/url
    > > Sent: Sunday, August 06, 2000 6:51 PM
    > > To: SeattleRobotics@egroups.com; basicstamps@egroups.com
    > > Subject: [noparse][[/noparse]basicstamps] Decoding 2 bit to 4
    > >
    > >
    > > Does anyone know of an IC that EXACTLY matches this truth table:
    > >
    > > IN OUT
    > > | a b | 1 2 3 4 |
    > > |
    |
    |
    > > | 0 0 | 1 0 0 0 |
    > > | 0 1 | 0 1 0 0 |
    > > | 1 0 | 0 0 1 0 |
    > > | 1 1 | 0 0 0 1 |
    > >
    > > The 74x195 & 74x155 have the outputs reversed from this, and I
    > > would have to
    > > use a set of inverters, and i REALLY needed to keep the # of devices to a
    > > minimum. So, if anyone knows of a device...
    > >
    > >
    > > Thanks in advance,
    > > Edward Kindler
    > >
    > >
  • ArchiverArchiver Posts: 46,084
    edited 2000-08-07 12:30
    74138 or equiv, decodes 3 bits, tie 1 bit off (low)

    Norm & Monda
    Cozy MK IV #202
    Ford V-6 Powered
    Original Message
    From: "Bruce Bates" <bvbates@u...>
    To: <basicstamps@egroups.com>
    Sent: Monday, August 07, 2000 1:06 AM
    Subject: Re: [noparse][[/noparse]basicstamps] Decoding 2 bit to 4


    > At 07:51 PM 8/6/00, you wrote:
    > >Does anyone know of an IC that EXACTLY matches this truth table:
    > >
    > > IN OUT
    > >| a b | 1 2 3 4 |
    > >|
    |
    |
    > >| 0 0 | 1 0 0 0 |
    > >| 0 1 | 0 1 0 0 |
    > >| 1 0 | 0 0 1 0 |
    > >| 1 1 | 0 0 0 1 |
    > >
    > >The 74x195 & 74x155 have the outputs reversed from this, and I would have
    to
    > >use a set of inverters, and i REALLY needed to keep the # of devices to a
    > >minimum. So, if anyone knows of a device...
    >
    > Either of the following decoders will ehibit the outputs you desire:
    >
    > CD4028 National HEF4028 Philips
    >
    > Both are BCD to Decimal, or Binary to Octal - Decoders. Both are a bit of
    > overkill, as they are wider than necessary, but so it is with 4-bit
    > requirements.
    > The National part has 4 input buffers and 10 output buffers (2/4, 3/8,
    > 4/10). Not sure about the Philips unit.
    >
    >
    >
    > >Thanks in advance,
    > >Edward Kindler
    >
    > Surely
    >
    > Regards,
    >
    > Bruce Bates
    >
    >
    >
    >
    >
  • ArchiverArchiver Posts: 46,084
    edited 2000-08-07 13:15
    norm doty wrote:
    >
    > 74138 or equiv, decodes 3 bits, tie 1 bit off (low)
    >
    > Norm & Monda

    74138 outputs are INVERTED of required.
    ACJacques

    >
    > > At 07:51 PM 8/6/00, you wrote:
    > > >Does anyone know of an IC that EXACTLY matches this truth table:
    > > >
    > > > IN OUT
    > > >| a b | 1 2 3 4 |
    > > >|
    |
    |
    > > >| 0 0 | 1 0 0 0 |
    > > >| 0 1 | 0 1 0 0 |
    > > >| 1 0 | 0 0 1 0 |
    > > >| 1 1 | 0 0 0 1 |
    > > >
    > > >The 74x195 & 74x155 have the outputs reversed from this, and I would have
    > to
    > > >use a set of inverters, and i REALLY needed to keep the # of devices to a
    > > >minimum. So, if anyone knows of a device...
  • ArchiverArchiver Posts: 46,084
    edited 2000-08-07 15:26
    thats right, sorry, i forgot.

    Norm & Monda
    Cozy MK IV #202
    Ford V-6 Powered
    Original Message
    From: "A.C.Jacques" <acjacques@i...>
    To: <basicstamps@egroups.com>
    Sent: Monday, August 07, 2000 8:15 AM
    Subject: Re: [noparse][[/noparse]basicstamps] Decoding 2 bit to 4


    > norm doty wrote:
    > >
    > > 74138 or equiv, decodes 3 bits, tie 1 bit off (low)
    > >
    > > Norm & Monda
    >
    > 74138 outputs are INVERTED of required.
    > ACJacques
    >
    > >
    > > > At 07:51 PM 8/6/00, you wrote:
    > > > >Does anyone know of an IC that EXACTLY matches this truth table:
    > > > >
    > > > > IN OUT
    > > > >| a b | 1 2 3 4 |
    > > > >|
    |
    |
    > > > >| 0 0 | 1 0 0 0 |
    > > > >| 0 1 | 0 1 0 0 |
    > > > >| 1 0 | 0 0 1 0 |
    > > > >| 1 1 | 0 0 0 1 |
    > > > >
    > > > >The 74x195 & 74x155 have the outputs reversed from this, and I would
    have
    > > to
    > > > >use a set of inverters, and i REALLY needed to keep the # of devices
    to a
    > > > >minimum. So, if anyone knows of a device...
    >
    >
    >
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