How do the EPROM work

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How do the EPROM work

Post by bitfogav » Sun Jun 13, 2010 11:05 pm

Hi Brad how do the eprom work on your POV project, I know you need to program it with your display data with a eprom programmer but I see your using one 74343 to address the first 8 pins and then another 74343 to address the other 8 pins, So im guesisng this is your 16bit address?.

so you start with 00000000 00000000 on the address bus for the 27C512.

then do you then set 0000000 00000001 on your adress bus to send your
byte of data say to the RED 74343 on the eprom output bus?

and then set 00000000 00000010 on your address bus to send your next
byte of data to the GREEN 74343 and so on?

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Post by brad » Mon Jun 14, 2010 8:14 am

Yes you're right, I have used two 74373's to essentially expand the 8-bits of PORTB into 16 bits.

So we start with

00000000 00000000

on the address bus, the data at this first address is a byte of red data. I then increment to

00000000 00000001

This address holds green, then increment once more to

00000000 00000010

And this holds one byte of blue data.

Each time we will be saving this data to each of the three 74373's. Once they all have their data, we can then enable the outputs which will turn on the relevant LED's.

A better way of going about things would be to use a serial eeprom although they are not as straight forward to use.

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Post by bitfogav » Mon Jun 14, 2010 10:21 am

Im thinking about using the eeprom memory on the microchip, the 16F648A as 256k of eeprom, which should be plenty for small displays and it is easier to erase and write using a PicKit2. It will also be easier to move the eeprom data to RAM when the microchip starts up, this allowing us to read the data faster :)

Am I right in saying that you have to erase the 27C512 eprom with a UV light every time you want to load it with more display data?

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Post by brad » Mon Jun 14, 2010 2:11 pm

bitfogav wrote:Im thinking about using the eeprom memory on the microchip, the 16F648A as 256k of eeprom, which should be plenty for small displays and it is easier to erase and write using a PicKit2. It will also be easier to move the eeprom data to RAM when the microchip starts up, this allowing us to read the data faster :)

Am I right in saying that you have to erase the 27C512 eprom with a UV light every time you want to load it with more display data?
Unfortunately it is only 256bytes of eeprom not Kbytes :(

as for the eprom's yes you are right you do have to expose them to UV light for about 20mins to erase them.

But EEPROM's however, you can erase them with the same programmer that you program them with so they are basically instant.

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Post by bitfogav » Tue Jun 15, 2010 2:54 am

Oh yeah it is only 256 bytes :( I guess serial eprom is one way to go then?

How have you managed it on your one chip POV system? :)

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Post by brad » Tue Jun 15, 2010 6:05 pm

Good question!

The one chip POV uses a nifty PIC18f4550 (Stacy are you hearing this!!!?)

18F's are great for holding onto a whole heap of data - just like eeprom really except you can store as much data as you want right there in program memory. Whether it be in one data table or dozens of seperate data tables. There is no need to worry about paging issues (as you do with 16f's)

That's why I could fit everything on one chip.

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Re: How do the EPROM work

Post by mshayan27 » Tue Jun 14, 2011 2:15 am

brad you are saying for corresponding color we have to enable an disable the corresponding latches but in your video i have seen than in 8 column pixels there are different colors in same column like there are blue and red in same column to show the italic text so how you give or enable 2 colors or more than 2 colors in one same column data? like for all red leds to glow i have to give "FFh"(with red latch enable) but if i want the 4 leds to be red and 4 leds to be blue when how to enable the and disable 2 latches or to give multicolour data?

hope you understand the question :)

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Re: How do the EPROM work

Post by brad » Tue Jun 14, 2011 8:15 pm

Each individual column is made up of Red, Green and Blue. Before we display any colors, we need to first send the data to the 74373's

We first send 8-bits of data to the Red 74373. then 8-bits to the green 74373 and then 8-bits to the blue 74373.

Once all three of them have their data, we enable the outputs of ALL 74373's and the LED's will light up all at once.

The key thing to remember is that we don't turn on any LED's until all data for one column has been saved to the 74373's

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