Decimal to binary

[Data888]

I have a circuit with a series of 8 decimal inputs. One line for each
possible input. I need to convert this to a binary number of 3 digits to
control the rest of the circuit. I can't seem to find an IC that does
this, they all go the other way. Any suggestions?

 

[Thomas C. Sefranek]

"Data888" <kcinSPAMBLOCK@bigfoot.com.au> wrote in message
news:40063B93.1040306@bigfoot.com.au...

I have a circuit with a series of 8 decimal inputs. One line for each
possible input. I need to convert this to a binary number of 3 digits to
control the rest of the circuit. I can't seem to find an IC that does
this, they all go the other way. Any suggestions?

Priority encoder. 74HC147

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| __O Thomas C. Sefranek WA1RHP@ARRL.net
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http://hamradio.cmcorp.com/inventory/Inventory.html
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[ANdre H]

I don't know if such a IC exist, ( I am not following ICs anymore ) but you
can build this with
exclusive Or gates.
b0 = c7 X c5 X c3 X c1
b1 = c7 X c2 X c3 X c6
b2 = c7 X c4 X c5 X c6

X stand for exclusive OR, b0,1,2 bits, c1-7 any of our 8 inputs (0 just set
all to zero)
Regards
"Data888" <kcinSPAMBLOCK@bigfoot.com.au> wrote in message
news:40063B93.1040306@bigfoot.com.au...

I have a circuit with a series of 8 decimal inputs. One line for each
possible input. I need to convert this to a binary number of 3 digits to
control the rest of the circuit. I can't seem to find an IC that does
this, they all go the other way. Any suggestions?

 

[Byron A Jeff]

In article <05mdnSFJkbkE8pvdRVn-tw@comcast.com>,
Thomas C. Sefranek <WA1RHP@ARRL.NET> wrote:
-
-"Data888" <kcinSPAMBLOCK@bigfoot.com.au> wrote in message
-news:40063B93.1040306@bigfoot.com.au...
-> I have a circuit with a series of 8 decimal inputs. One line for each
-> possible input. I need to convert this to a binary number of 3 digits to
-> control the rest of the circuit. I can't seem to find an IC that does
-> this, they all go the other way. Any suggestions?
->
-Priority encoder. 74HC147

Just be aware that since it is a priority encoder that only the highest
priority input will be encoded. So if input 4 and input 6 are both active,
then the output will show 6.

BAJ

 

[R. Steve Walz]

Data888 wrote:

I have a circuit with a series of 8 decimal inputs. One line for each
possible input. I need to convert this to a binary number of 3 digits to
control the rest of the circuit. I can't seem to find an IC that does
this, they all go the other way. Any suggestions?
---------------------------

Assuming your 8 outputs are logic-LO:

You route backward guard diodes from each of the 8 outputs to three
pullup resistors, so that they pull these outputs LO when they should
be LO: Cheap open-collector decoder. The earliest ROM was made that
very way.

Example, from 7 you route NO diodes, you want the outputs HI, "111",
but from 0 you route diodes to all three outputs you want to go LO,
from 5 you route only one diode to the 2's bit, to make "101", and
from 2 you route two diodes to the 4's and the 1's bit, etc.

If your outputs are open-collector-LO or active-LO,like a74LS138, then
the decoder for 8 values, 0 through 7, takes 3+2+2+1+2+1+1+0=12 diodes
and three 1K resistors.

-Steve
--
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