74HC datasheet, 74HC pdf, 74HC data sheet, datasheet, data sheet, pdf, Philips, 8-bit shift register with input flip-flops. 74HC Counter Shift Registers are available at Mouser Electronics. Mouser offers inventory, pricing, & datasheets for 74HC Counter Shift Registers. (Note: Microdot may be in either location). See detailed ordering and shipping information in the package dimensions section on page 2 of this data sheet.

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Sometimes you’ll end up needing more digital input than there are pins on your Arduino. Using a parallel to serial shift register you can collect information from 8 or more switches while only using 3 of the pins on your Arduino. This means you can read the state of up to 8 digital inputs attached to the register all at once.

This is called Asynchronous Parallel Input. This pin should be connected to an adtasheet pin on your Arduino Board, referred to as the data pin.

The transfer of information on the data pin is called “Synchronous Serial Output” because the shift register waits to deliver linear sequence of data to the Arduino until the Arduino asks for it.

Synchronous Serial communication, either input or output, is heavily reliant on what is referred to as a clock pin. The clock pin is the metronome of the conversation between the shift register and the Arduino, it is what keeps the two systems synchronous.


The third pin attached to the Arduino is a “Parallel to Serial Control” pin.

Arduino – ShiftIn

It is referred to as a latch pin. When the latch pin is HIGH the shift register is listening to its 8 parallel inputs. When the latch pin is LOW, it listens to the clock pin and passes information serially. That means every time the latch pin transitions from HIGH to LOW the shift register will start passing its most current switch information.

There is more information about shifting in the ShiftOut tutorial.

Datasheet «MC54/74HC597»

Before you start wiring up your board here is the pin diagram of the CD from the Texas Instruments Datasheet. In this example you’ll add a second shift register, doubling the number of input pins while still using the same number of pins on the Arduino. If supplementing your Arduino with fatasheet additional 8 digital inputs isn’t going to be enough for your project, you can have a second CD pass its 74h5c97 on to another CD which will stream all 16 bits of information to the Arduino.

If you know you will need to use multiple shift registers like this, check that any shift registers you buy can handle Synchronous Serial Input as well as the standard Synchronous Serial Output capability.

74HC Datasheet pdf – 8-bit shift register with input flip-flops – Philips

Synchronous Serial Input is the feature that allows the first shift register to receive and transmit the serial output from a second one. The example below details how to use this system. Within reason, you can keep extending this daisy-chain of shift registers until you have all the inputs you need.


Two of these connections simply extend the same clock and latch signal from the Arduino to the second shift register yellow and green wires. The blue wire is going from the serial out pin pin 9 of the first shift register to the darasheet data input dataxheet 14 of the second register.

Notice that there is one momentary switch and the rest are toggle switches. This is because the code examples will be using the switches attached to the second shift register as settings, like a preference file, rather than as event triggers.

74HC597 Datasheet PDF

The one momentary switch will be telling the microcontroller that the setting switches are being changed. Serial Output Pins from different steps in the sequence. Q7 is a pulse behind Q8 and Q6 is a pulse behind Q7.

Q8 is the only one used in these examples.