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how to make rom memory circuit for microcontroller

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Parth86

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I want to make rom memory circuit for controller I don't know actually I have read some where that rom make form combining latches and encoder but I am confused which circuit make rom of controller
i have following question on rom memory (which component and which logic circuit make rom memory)

1)how to decide which logic circuit is used to make rom memory
2)what circuit component I need to make rom memory (i think basic flip flop and latches)
3) what should I need to know before to make circuit of rom memory

please anyone give me idea how to make rom memory for controller
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The main question is "which micocontroller?" as there are many different types, of which almost all have the program memory already included on the chip die. This should answer your question number one.
As for number two, you should know that you cannot make a non-volatile memory just from flip flops and latches. You can make non-volatile truly read-only memory from a bunch of ORs and ANDs, but it will be hard wired and non-reprogramable.
As for number three, you need to know all of the above, plus a lot more I suppose.
 
Hi,

When you "make a ROM" how low do you want to go?

For example, you can make a ROM with diodes.
 
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Hi Ian,

I like the switch addition that adds flexibility. The one i was talking about was hard wired. Still need diodes unfortunately, and an address decoder of some sort. Diodes like 1N4148 should work pretty well as they are fast and small and cheap. Logic levels have to be carefully checked that's all, maybe Schottky diodes would be better.
 
hmmm.. I am curious, why would any body (in late 2013) want to "build a ROM" ?

ROM stands for Read Only Memory, do you mean a One Time Programmable?

Give us a little more info on what you are trying to do? What micro controller are you using (or want to use) ?
 
Arduino Memory Shield $14.90
https://www.mpja.com/SD-Card-Shield-Seeeduino-Module/productinfo/30428%20MP#

Standardized and stackable shield board compatible with the Arduino I/O Pins. Need more storage? Module supports SD <16G,SDHC <16G and uHD<2G. Fully compatable with existing Arduino SD card software library. Uses the SPI port to communicate leaving the Arduino I/O available. Includes Grove UART and I2C ports.
You should be able to use it with any micro controller.
 
I want make rom memory with TTL logic I have read that rom is made with flip flop circuit can I use latches to make rom memory or which circuit involve to make rom memory
 
where did you read that? can we get a link?

Any circuit you will build with ttl logic and latches, etc, will lose all its information (stored data) when you turn power off.

IMHO, this is not a ROM.. right?
 
I want make rom memory with TTL logic I have read that rom is made with flip flop circuit can I use latches to make rom memory or which circuit involve to make rom memory

Hello,

Are you perhaps talking about a "RAM" rather than a "ROM" ?

I ask this because a RAM may use Flip Flops but a ROM uses other means, unless it is a ROM that uses a battery back up to hold the information when the power is removed.

The difference between the RAM and ROM is that the RAM losses memory when the power is removed but the ROM does not. And more strictly speaking, a ROM is not programmable it is only readable. A RAM is programmable.
Some ROM's can be programmed but then they are called EPROM's, which means they are electrically programmable. A regular ROM is either built that way at the factory or else it started out as a EPROM at the factory and was programmed at the factory and reaches the consumer as a ROM because it has already been programmed and there is no means to reprogram.
There is also the PROM, which is a one time programmable ROM which reaches the consumer in an unprogrammed state, and the user programs it one time and one time only and then it becomes a ROM because after that it can only be read from (RO=read only, M=memory).


So maybe rethink what it is you really want to build.
 
Here is a book ... it is a few years old ... but seems adequate in this subject area.
It looks like it is free ... I don't actually know how that works though.
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You will also need to know how many memory locations... how many data bits, and as Kubeek said, which micro you want to interface to. Hardware can add up fast. Can't you still buy EPROMs? You can also used tristate bus drivers, one byte each, but depending on number of memory locations, HARDWARE CAN ADD UP FAST.

I was involved in one project (for a police cruiser) that interfaced serially to a camera. The speed of the interface was such that a micro could not spit out the bitstream fast enough so we used parallel to serial shift registers with a preset bit pattern input to each for a single command. This was practical since there were only 6 commands.
 
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