Film selection is a single chip subject vocabulary, which can be understood as film selection.Chip Select Generallyaddress spaceWhen, bylogical circuitGenerated.staydigital circuit In design, the open circuit input pin is generally shown asHigh levelTherefore, the chip selection signal is aLow level。
Selection:verbMonolithic subject vocabulary can be understood as chip selection.For example, there are many chips hanging on the same bus (like many peripherals in a computer are hanging on the bus), but sometimes we need to transmit data, addresses or commands to a specific chip independently. At this time, we need a signal to tell the chips hanging on the bus which chip these data and addresses are sent to.In that case, other chips will be "indifferent" to these signals, and the target chip will know that these data are transmitted to itself to respond.This signal is calledChip Select CS (chip select) or SS（slaveselect)。The term "film selection" is derived from this, which refers to the use ofAnd door、OR Gate、Non gateTo determine which parts areEnter the working state。
Programmable interface chips have a chip switch, usually CE（ChipEnable) or CS (Chip Select) means that only when the input terminal is in effectlevel, the interface chip enters the circuitworking condition , realize theI/O。The chip selection terminal usually uses the AO addressdecoderTherefore, chip selection is also the process of selecting the interface chip by the designated AO address to make it enter the circuit working state.
Figure 1
As shown in Figure 1, if a slave chip orSlave deviceIf the SS pin of (slave) is inactive (usually low level), then the slave chip or slave device is equivalent to a deaf person, and will not affect any externalInput signalRespond.If one of the slave chip's SS pins is active, it can hear external input signals and receive or respond.In Figure 1, MISO is the channel for data transmission from the chip to the master chip, MOSI is the channel for data transmission from the master chip to the slave chip, and SCLK is the clock channel (master chip → slave chip).
Chip selection of memory chips
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storageIt usually consists of a certain number of chips.
CPUTo achieveStorage unitYou must first selectMemory chip, that is, film selection;Then click theAddress codeSelecting the corresponding storage unit for data access is called word selection.The on-chip word selection is N low bits sent by the CPUAddress lineThe address line is directly connected to the address input terminals of all memory chipsChip Select It is mostly generated after decoding the high bit address.
Line selection method:
Line selection is to use divisionOn-chip addressingThe external high bit address line is directly connected to the chip selection end of each memory chip. When the information of an address line is 0, the corresponding memory chip is selected.These chip selection address lines can only have one valid bit each time they are addressed, and it is not allowed to have multiple valid bits at the same time, so that only one chip can be selected at a time.The line selection method cannot make full use of the systematicstorageSpace, putaddress spaceIt is divided into mutually isolated areas, which brings some difficulties to programming
wholedecodingAll high bits except intra chip addressingAddress lineAll as addressesdecoderThe input of the decoder and the output of the decoder are used as chip selection signals of each chip, and they are respectively connected toMemory chipTo realize the selection of memory chips.The advantage of the full decoding method is that the address range of each chip is unique, continuous, easy to expand, and does not produce address overlapping memory areas. However, the full decoding method requires higher decoding circuits
Partial decoding method: the so-called partial decoding method uses a part of the high bit address other than the on-chip addressing to decode and generateChip Select , partial decoding will produce address overlap.
