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Tech You How To 74HC595 Shift Registers

2017-06-20 15:50:45 | 日記

74HC595 and 74hc164 chip system is commonly used in the serial signal into a parallel signal, commonly used in a variety of digital control and dot matrix screen driver chip, the use of 74HC595 can save the microcontroller mcu Io mouth resources, with three io can control the pin of the 8 digital tube, it also has a certain driving ability, you can avoid the transistor and other amplification circuit, so this chip is driving the digital tube artifact.

Here I would like to introduce 74HC595 work principle:

74HC595 data side:

QA - QH: eight parallel output, you can directly control the digital tube 8 segments.

QH ': Cascade output. I took it to the next 595 SI side.

SI: Serial data input.

74hc595 console instructions:

/ SCLR (10 feet): low level to clear the shift register data. Usually I'll take it to Vcc.

SCK (11 feet): data shift at the rising edge of the data register. QA -> QB -> QC -> ... -> QH; falling edge shift register data unchanged. (Pulse width: 5V, more than a few tens of nanoseconds on the line. I usually choose microsecond)

Control shift register

SCK rising edge data shift SCK falling edge data hold

RCK (12 feet): the rising edge of the data when the register register into the storage register, the falling edge of the register register data unchanged. Normally I set RCK low, and when the shift is complete, a positive pulse is generated on the RCK side (more than a few tens of nanoseconds at 5V, and I usually select microseconds) to update the display data.It is hot seller for electronic component distributors.

RCK rising edge shift register data into memory register RCK falling edge memory register data unchanged

/ G (13 feet): High output (high impedance state) is disabled. If the microcontroller pin is not tight, with a pin to control it, you can easily produce flicker and extinguish the effect. Than through the data port shift control to save time and effort.
Note: 74164 and 74595 function similar to the 8-bit serial input to the parallel output shift register. 74164(74hc595 arduino) drive current (25mA) than 74595 (35mA) to be small, 14 feet package, the volume is also smaller.
The main advantage of the 74595 is that it has a data storage register, and the data at the output can remain unchanged during the shift. This is very useful in the case of slow serial speed, digital tube is not a sense of flash.

Compared with 74hc164 only data clear side, 74hc595 more than the output can / disable the control end oe, you can make the output high impedance state. So it is more convenient to use this chip

74HC595 is an 8-bit shift register and a memory, tri-state output function. The shift register and the memory are separate clocks. The data is entered on the rising edge of SHcp (see timing diagram) and entered in the memory register on the rising edge of STcp (see timing diagram). If the two clocks are connected together, they are shifted

The register is always a pulse earlier than the memory register. The shift register has a serial shift input (Ds), and a serial output

(Q7 '), and an asynchronous low-level reset, the memory register has a parallel 8-bit, 3-state bus output,

At OE (low), the data stored in the register is output to the bus.

Reference: how to test cr123a

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