Memory structure

Memory is where data is stored. It uses the level to store data, that is to say, it actually stores the level of high and low, rather than the number 1234 that we are used to think. In this way, a mystery is solved, and there is nothing mysterious about computers.

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Figure 1

Let’s look at Figure 1. There is such a memory in the single chip microcomputer. This is the schematic diagram of a memory: a memory is like small drawers one by one. There are eight small grids in a small drawer. Each small grid is used to store “electric charge”. The electric charge is transmitted or released through the wires connected with it. As for how the electric charge is stored in the small grid, we don’t have to worry about it, If you can think of a wire as a water pipe, the electric charge in a small lattice is like water, that’s easy to understand. Each small drawer in memory is a place for data, which we call a “unit”.

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Figure 2

With such a structure, we can start to store data. If we want to put a data 12, that is, 000011100, we just need to fill the second and third cells with charges, and let go the charges in other cells (see Figure 2). But the problem comes out. Look at Figure 1. A memory has many cells, and the lines are in parallel. When the charge is put in, the charge will be put into all the cells. When the charge is released, the charge in each cell will be released. In this way, no matter how many cells there are in the memory, only one number can be put. Of course, this is not what we want. Therefore, There is a control line on each cell. If I want to put the data into any cell, I will give a signal. The control line of this cell will turn on the switch, so that the charge can flow freely. However, there is no signal on the control line of other cells, so the switch will not be turned on and will not be affected, As long as you control the control lines of different units, you can write different data to each unit. Similarly, if you want to take data from a unit, you only need to turn on the corresponding control switch.

Memory decoding

So, how do we control the control line of each unit? This is not simple. Just lead the control line of each cell to the outside of the integrated circuit? It’s not that simple. There are 65536 cells in a 27512 memory. If every wire is led out, the IC will have more than 60000 pins? No, what should I do? Try to reduce the number of lines. We have a way to call it decoding. Let’s give a brief introduction: one line can represent two states, two lines can represent four states, three lines can represent several States, and how many lines are needed to represent 256 States? Eight kinds, eight lines, so we only need 16 lines to represent 65536 states.

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Figure 3

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