Dynamic memory has only one input data line per chip, and only eight address pins. In order to form 64K addresses, an address formation circuit must be specially designed between the system address bus and the chip address lead. The system address bus signal can be added to the pins of 8 addresses in time, and the memory unit in the chip is selected by the internal row latch, column latch and decoding circuit, and the latch signal is also generated by the external address circuit. When reading data from the DRAM chip, the CPU first adds the row address to A0-A7 and then sends the RAS latch signal, the falling edge of which locks the address inside the chip. Then the column address is added to the A0-A7 of the chip, and the CAS latch signal is sent, and the column address is locked inside the chip at the falling edge of the signal. Then hold WE=1, and the data is output and held for the duration of the CAS. When data needs to be written to the chip, the row address successively locks RAS and CAS inside the chip, and then, with the effect of WE, plus the data to be written, the data is written to the memory unit in the entry. Since the capacitor cannot keep the charge unchanged for a long time, the memory unit of the dynamic memory circuit must be reread periodically to keep the charge stable, this process is called dynamic memory refresh. DRAM refresh in PC\/XT machines is implemented using DMA. First, the counter 1 of the programmable timer 8253 is applied to generate a DMA request every 1 (5) 12μs, which is added to channel 0 of the DMA controller. When the DMA controller's channel 0 request gets a response, the DMA controller sends a signal to the refresh address and performs a read operation on the dynamic memory, refreshing one line each time it reads.
1, the unit in sram is a number of switches to form a trigger, which can stably store 0, 1 signals, and can change the stored value through timing and input signals.
2, dram, mainly according to the power on the capacitor, when the power is large, the high voltage means 1, and on the contrary, the 0
chip is composed of a large number of these units, so it can store data.
Programs are just data. The circuit reads data from the memory chip, and according to the timing of the circuit and the logic operation of the circuit, the data of other storage units can be modified