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What do the Address and Data Pins do on an EPROM?


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Im trying to learn a little bit about how EPROMs work and I don't quite understand how the Address and data pins work.  The address pins(address bus) recieves the address that the computer or whatever is reading it supplies, and the data(data bus) pins outputs the value that is stored in the byte through the 8 pins(8 bits) right?  Can some make this a little clearer for me?  Also, if anyone has any good web-pages regarding this material I'd really like to take a look at it.  Thanks!

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Hi V8meathead

Several EPROM's are sometimes used in a system, this is why you find the pins /E and /G, the / means that they are active low (confirmed also by the small circle) and are used to (/E) enable a particular chip so that it can be read from or whilst programming, can be written to. The /G is an output enable.  Normally all EPROM's will have their /G pins connected to 0v and the /E pin enabled individually so that data from only one chip will be output onto a common databus.  This means that for every EPROM in this system every Q0 is joined together and all Q1's etc., forming a databus. Whilst the /E input is high (=1) data out is tristated or invisible.

Whilst there are many other ways of doing this, consider what would happen if you had programmed the bit pattern for a 7 segment LED as data in each of the lowest 16 addresses?

If you address location 0, the bit pattern could be used to show 0 on a display, location 1 would show 1 and so on...

It's also possible to program quite complex test sequences using a single EPROM, imagine a parallel counter which is attached to the address pins of the EPROM.  At each clock transition, the address increases by 1 giving a different byte on the data output - that byte is then used to do something with other logic and can inhibit the clock until the system is ready for the next address.

Hope this helped

Ed

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