2020-11-05
1. Buffer principle-introduction
Buffer is the abbreviation of buffer register, which is divided into input buffer and output buffer. The function of the former is to temporarily store the data sent by the peripheral so that the processor can take it away; and the function of the latter is to temporarily store the data sent by the processor to the peripheral. With the numerical control buffer, the high-speed working CPU can coordinate and buffer the slow-working peripherals to realize the synchronization of data transmission. Since the buffer is connected to the data bus, it must have a three-state output function.
2. Buffer principle-classification
There are two types of buffers, commonly used buffers (often said buffers) and tri-state buffers. The conventional buffer always outputs the value directly, and is used in the circuit system to advance the current to a higher level. In addition to the functions of the conventional buffer, the tri-state buffer also has an optional cartoon input terminal, denoted by E. There are different output values when E=0 and E=1.
When E=1, strobe, its input is directly sent to the output;
If E=0, the buffer is blocked, no matter what value is input, the output is always high impedance, denoted by Z. The high impedance state can make the current drop low enough so that the output of the image buffer is not connected to anything.
3. Buffer principle
In the design of the CPU, the DC load capacity of the general output line can drive a TTL load. During the connection process, an address line or data line of the CPU may be connected to multiple memory chips, but the memory chips are all MOS The circuit is mainly composed of capacitive load, and DC load is much smaller than TTL load. So in a small system, the CPU can be directly connected to the memory, but in a large system, a buffer is needed.
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