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basics | Binary to BCD converter IC?


There are 14 messages in this thread.

You are currently looking at messages 1 to 10.

Binary to BCD converter IC? - ivanatora - 2008-01-16 04:20:00

Hello,
I'm searching for an IC which can convert binary input to BCD code.
I have a TC77 temperature sensor, which provides data to 8-bit shift
register, and finally I have 8 bits in complementary code for negative
temperatures, and straight code for positive temperatures. Let's put
aside the negative numbers for now and concentrate on simple binary to
BCD converter. I want to put that reading on a 7-segment indication
via 7447 driver.
So long for now I've found in Google ICL74185 as binary to BCD
convertor, but I will need 2 or 3 hooked together for converting 8-bit
number. Also I can't find that IC anywhere on our stores and it seems
it is not in production anymore.

The other question is - is there a IC for converting the complimentary
code into straight code?

I don't want to use microcontrollers.

Regards, Ivan.

Re: Binary to BCD converter IC? - Stephen J. Rush - 2008-01-16 05:44:00

On Wed, 16 Jan 2008 01:20:26 -0800, ivanatora wrote:

> Hello,
> I'm searching for an IC which can convert binary input to BCD code. I
> have a TC77 temperature sensor, which provides data to 8-bit shift
> register, and finally I have 8 bits in complementary code for negative
> temperatures, and straight code for positive temperatures. Let's put
> aside the negative numbers for now and concentrate on simple binary to
> BCD converter. I want to put that reading on a 7-segment indication via
> 7447 driver.
> So long for now I've found in Google ICL74185 as binary to BCD
> convertor, but I will need 2 or 3 hooked together for converting 8-bit
> number. Also I can't find that IC anywhere on our stores and it seems it
> is not in production anymore.
> 
> The other question is - is there a IC for converting the complimentary
> code into straight code?

A small (256 bytes) PROM can be programmed to convert 8-bit twos-
complement to two BCD digits and a sign bit, but you'd lose some 
precision.  A wider PROM could supply 12 BCD bits and a sign.  Somebody 
probably offers it preprogrammed; National Semiconductor used to have a 
bunch of specialized decoders based on the same  mask ROM, back in the 
Z-80 era.  Converting twos-complement to natural binary can be done with 
gates, but the minimum-package-count solution is probably a small 
microcontroller.  Some of them, especially the low-speed grades, have 
become absurdly cheap.  Most of them have a serial input, so you wouldn't 
need the shift register.

Re: Binary to BCD converter IC? - 2008-01-16 12:25:00

ivanatora <i...@gmail.com> writes:
> I don't want to use microcontrollers.

This was recently covered in detail.  How about a CPLD?  Program it
once, treat it like a complex logic chip.  XC9536's cost about $1 at
digikey.

Re: Binary to BCD converter IC? - Bob Monsen - 2008-01-17 01:38:00

"DJ Delorie" <d...@delorie.com> wrote in message 
news:x...@delorie.com...
>
> ivanatora <i...@gmail.com> writes:
>> I don't want to use microcontrollers.
>
> This was recently covered in detail.  How about a CPLD?  Program it
> once, treat it like a complex logic chip.  XC9536's cost about $1 at
> digikey.

How much does the programmer cost? I looked into CPLDs a while back, and the 
programming algorithm was proprietary, meaning I'd have to shell out a few 
hundred bucks for a programmer.

Regards,
 Bob Monsen


Re: Binary to BCD converter IC? - 2008-01-17 02:54:00

"Bob Monsen" <r...@gmail.com> writes:
> How much does the programmer cost? I looked into CPLDs a while back,
> and the programming algorithm was proprietary, meaning I'd have to
> shell out a few hundred bucks for a programmer.

The Xilinx tools are free, and they have app notes that tell you how
to run the jtag yourself for embedded ISP, and provide a tool to
compress the bitstream into something easily parsable (and
documented).

Me, I'm wiring mine up to a small mcu module I already have[*], so the
cost to me for the programmer is zero.  There are schematics for the
Parallel III cable if you want to build it; it's a connector and a
couple of TTL chips.

Total cost to me to have a XC9536XL CPLD: $1.


[*] http://www.delorie.com/electronics/usb-gpio/

Re: Binary to BCD converter IC? - 2008-01-23 01:01:00

DJ Delorie <d...@delorie.com> writes:
> XC9536's cost about $1 at digikey.

Just FYI I did a trial synthesis (by first! :) of this, and it fits
into the XC9572 but not the XC9536.  So, it's $2 instead of $1.

Re: Binary to BCD converter IC? - 2008-01-23 23:46:00

DJ Delorie <d...@delorie.com> writes:
> Just FYI I did a trial synthesis (by first! :) of this, and it fits
> into the XC9572 but not the XC9536.  So, it's $2 instead of $1.

More trials.

If you want a multiplexed display (three digit drivers, seven segment
drivers, clock input), it fits easily into a XC9536.

If you want separate digits (i.e. 21 segment drivers) but don't mind
providing a clock (full update in three clocks), that can fit into an
XC9536 too.  This works because there's only one 7-segment decoder
block, which is shared across the three output modules.

It looks like there's enough remaining cells to implement leading zero
blanking, too.

Not that I've actually tried any of these in hardware :-)

Re: Binary to BCD converter IC? - ivanatora - 2008-01-27 04:09:00

I'm back again.
I've searched a lot and find no easy way to convert parallel binary
into BCD, so I'm reconsidering using a microcontroller. They are
pretty cheap indeed, and a friend of mine just built a PIC16
programmer. Me and him are not so bad in C and asm, so we could make
of that good learning project :)

Re: Binary to BCD converter IC? - Ken Fowler - 2008-01-27 21:12:00

On 27-Jan-2008, ivanatora <i...@gmail.com> wrote:

> Xref: number1.nntp.dca.giganews.com sci.electronics.basics:284450
>
> I'm back again.
> I've searched a lot and find no easy way to convert parallel binary
> into BCD, so I'm reconsidering using a microcontroller. They are
> pretty cheap indeed, and a friend of mine just built a PIC16
> programmer. Me and him are not so bad in C and asm, so we could make
> of that good learning project :)

I believe someone pointed out that an easy way to convert binary to BCD is
to store the BCD values in EPROM(s) and use the binary as the address.  I
once wrote an ASM Macro to generate the BCD values for storing in a HEX
file to program the EPROM.  You need four output bits of EPROM for each BCD
digit.  For eight bit binary you need two eight bit wide EPROMs.

Ken Fowler

Re: Binary to BCD converter IC? - ivanatora - 2008-02-08 00:59:00

> I believe someone pointed out that an easy way to convert binary to BCD is
> to store the BCD values in EPROM(s) and use the binary as the address.  I
> once wrote an ASM Macro to generate the BCD values for storing in a HEX
> file to program the EPROM.  You need four output bits of EPROM for each BCD
> digit.  For eight bit binary you need two eight bit wide EPROMs.
>
> Ken Fowler

In that way what would happen to the number 1110 (14) for example?
There is no corresponding (readable) BCD code for that, and two BCD
digits must be emitted - '1' and '4'.

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