0-99 Binary to BCD converter

Well, you can do it in one chip if you're allowed to use a microcontroller ;-)

On Apr 2, 9:22 pm, DJ Delorie wrote: > Well, you can do it in one chip if you're allowed to use a > microcontroller ;-)

Less horsepower than that. (E)PROM look up table. Too bad this isn't allowed either.

GG

Wouldn't you need a counter in addition to the (E)PROM? (Making it two chips)

Regards, Gilles.

the lowest bit will be easy after that it gets interesting.

one way would be a 128 byte rom :)

I see two possible approaches,

one is massed logic, just figure out how each output bit is determines by the input bits..

the other is synchronised counters, drive two counters one that counts base 10 and drives the display and another that counts in bibary and you compare with the input.

or even better a presettable binary down counter, and a two-digit BCD up counter.

look up these (cmos 4000 family) part numbers. 4553 4516 4518 4029 download the datasheets and see what you can do. eg type "4553 datasheet" in the google search box and see where it takes you.

Bye. Jasen

Sound like your prof is playing a trick on you. (Did you get this assignment on April 1?)

The conventional approach (way back when people actually did these things with discrete chips) is to use decade counters, such as the 7490, which can be cascaded to count as many digits as you like. Each 7490 sends its output to one 7447. No adders needed!

Best regards,

Bob Masta D A Q A R T A Data AcQuisition And Real-Time Analysis

Scope, Spectrum, Spectrogram, Signal Generator Science with your sound card!

The brute force way is to load the seven bit binary number into a binary down-counter and at the same time to clear two BCD counters connected in cascade. Then clock them both with the same clock and stop counting when the binary counter gets to zero. The BCD counters will now have as outputs the BCD value of the binary number loaded into the down-counter.

--
JF

Nope. seven address bits, eight data bits - the address is the "input value" and the resulting data is the pre-computed BCD-decoded value.

You could even pre-compute the 7-segment decode, with seven address bits and 14 data bits.

!

really? Is this the way you'd do it?

Why wouldn't you use a couple of 74LS185 to do direct conversion?

sorry - link...

lots of answers from other people here (mostly jokes, right?)... but.. the best way to do it is with 2x 74LS185 - they are designed exactly for this job.

Forget about counters and stuff, these two chips correctly arranged will provide the correct BCD outputs to feed into your 7447s - i.e exactly what you want.

schreef in bericht news: snipped-for-privacy@p77g2000hsh.googlegroups.com...

One thing is not clear to me: Do you have a 7-bits binary counter (so you need to convert from binary to BCD to 7-segment) or do you need a BCD counter that outputs directly in 7-segment? Or even some other scheme?

As for using full adders for conversion, suppose "In" to be the binary input and "Out" to be the BCD output, you get:

In

oops... 3x 74ls185, not two - soz

The 74LS185 is a ROM chip, pre-programmed with the results. This is one of the "joke" solutions you refer to.

You were correct the first time, it only takes 2x to do the numbers 0 - 99 with a 7 bit binary input. Good luck finding a supplier, I could hardly find a datasheet. ;-)

thanks to everyones input, Eproms I don't know how to use and I'm almost certain 74Is185 have been discontinued.

blimey! you are right - rare as chicken thingies.

doing it with an eprom is quite easy and, Ithink, the best option.

eproms work by you providing a binary address (i.e. what you are currently providing to you 7447 and giving out a piece of data (8 bits

- just right to feed 2x 7447)

you will need to make sure that whatever eprom you use, you ensure the CS is low and the output (OE or RD) on some is also enabled all the time.

then you need to work out what combination of data patterns comes out... here is a list of the data for each address... assuming you are driving two 7447, the Left most digit driven from the least significant 4 bits (D0 - D3)

all addresses and data are in HEX.

connect your 7 bits of data to A0-A6 and connect all other address lines to 0V

should have this up and running is 2 hours max - assuming you have access to an EPROM programmer

here is a list of the data for each address... assuming you are driving two 7447, the Left most digit driven from the least significant 4 bits (D0 - D3)... Not really my habit to spoon feed, but trust me - this will lead to greater things once your creative juices start flowing.

all addresses and data are in HEX.

ADDR DAT =======

0000 00 0001 01 0002 02 0003 03 0004 04 0005 05 0006 06 0007 07 0008 08 0009 09 000A 10 000B 11 000C 12 000D 13 000E 14 000F 15 0010 16 0011 17 0012 18 0013 19 0014 20 0015 21 0016 22 0017 23 0018 24 0019 25 001A 26 001B 27 001C 28 001D 29 001E 30 001F 31 0020 32 0021 33 0022 34 0023 35 0024 36 0025 37 0026 38 0027 39 0028 40 0029 41 002A 42 002B 43 002C 44 002D 45 002E 46 002F 47 0030 48 0031 49 0032 50 0033 51 0034 52 0035 53 0036 54 0037 55 0038 56 0039 57 003A 58 003B 59 003C 60 003D 61 003E 62 003F 63 0040 64 0041 65 0042 66 0043 67 0044 68 0045 69 0046 70 0047 71 0048 72 0049 73 004A 74 004B 75 004C 76 004D 77 004E 78 004F 79 0050 80 0051 81 0052 82 0053 83 0054 84 0055 85 0056 86 0057 87 0058 88 0059 89 005A 90 005B 91 005C 92 005D 93 005E 94 005F 95 0060 96 0061 97 0062 98 0063 99 0064 FF 0065 FF 0066 FF 0067 FF 0068 FF 0069 FF 006A FF 006B FF 006C FF 006D FF 006E FF 006F FF 0070 FF 0071 FF 0072 FF 0073 FF 0074 FF 0075 FF 0076 FF 0077 FF 0078 FF 0079 FF 007A FF 007B FF 007C FF 007D FF 007E FF 007F FF

instead of doubling up your eproms (or using a big beastie) why not just use A7 as a strobe and provide both seven seg data on the single data outputs.

so use A7 to toggle between display segments

what? a two chip "discrete TTL" solution to do exactly what the OP wants - fail to see the joke. The internal construction of the chip has no bearing...