8 Bit number to 3 seperate 7-segment LED displays

[Spehro Pefhany]

Can you still buy plain old ROMs any more? I checked digikey but the
smallest EPROM they had was 1kx8 for $13, or some 2kx8 eeprom for $4.

ST M27C512 $3.24 each. OTP version: $1.71 each (99 cents in 250)

They did have a 44 pin CPLD for $1 though.

Best regards,
Spehro Pefhany

 

[Rich Grise]

Can you still buy plain old ROMs any more? I checked digikey but the
smallest EPROM they had was 1kx8 for $13, or some 2kx8 eeprom for $4.

They did have a 44 pin CPLD for $1 though.

Yikes! I guess I've been out of the loop too long.

But, it's true, if you can make a 256 X 21 ROM in(on?) a CPLD, (or
FPGA, or any of the other gate arrays) then you should have it
practically done already.

Of course, the 21 bits would be the seven segments for the three
displays.

It'd take another couple of bits to do decimal points, but that
would change the scope of the assignment, so don't bother.

Cheers!
Rich

 

[Andy]

The number will be coming from an EPROM and won't change once it's
been set. The 8 bits will be converted to decimal, so you're correct
in your assumption.

Why don't you program the EPROM(s) to output BCD, instead of binary?

 

[Eeyore]

Eg.
http://www.atmel.com/dyn/resources/prod_documents/doc1615.pdf
32 I/O, USD 1.23 (62p) in 100.

Thanks Spehro, that's quite interesting.

I guess it's something I ought to look into further.

Graham

 

[GPG]

---
An old brute-force way to do it is to simultaneously load the binary
number into an 8 bit down-counter and clear three BCD counters, then
use the same clock to count the binary number down to zero while
up-counting the BCD counters. Stop counting when the binary counter
gets to zero, and the BCD counters will have accumulated the BCD
equivalent of the original binary number.

http://www.geocities.com/gpg212/binbcdckd.gif

 

[vincent.thiernesse]

Hello,

I have done this recently. (need a 74ls47, three transistors and a PIC)

I can give a schematics, a typon, etc...

tell me

regards

Vincent

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[Joseph2k]

Good afternoon,

I was wondering if anyone can give me some ideas on how to take an8-bit number and display it on 3 LED displays.

I would be extremely grateful if you could give me a push in the right
direction.

many thanks,

Sean

Pick an EPROM, preferably cheap. We will program about 1 kib. Shift
up your 8 bit value (or not, bit position
is not that important here) you need a 2 bit counter to cycle the
addresses for readout. Encode the translated
value to the 8 bits to directly seven segment displays. Use state 00
to read the value and the succesive
states to display the three digits. With an oscillator, maybe half a
dozen parts.

Joseph