APPLICATION NOTE
Increase the Number of Outputs on a Microcontroller
Microcontrollers often have a very limited number of GPIO pins. Serial-in parallel-out shift registers can be used to output to a large number devices while only utilizing a few GPIO pins from the controller.
See more about this use case in the Logic Minute video Increase the Number of Outputs on a Microcontroller.
Design Considerations
- Serial input data (BRin) must be faster than the desired output data rate (BRout) based on the number of output bits (N) by this equation: BRin (Mbps) = BRout (Mbps) × N
- The clock input controls the rate at which data is loaded into the shift register, Fclk (MHz) = BRin (Mbps)
- For more outputs, shift registers can be daisy-chained together
- [FAQ] What is the default output of a latched device? (Flip-Flop, latch, register)
- Ask a question on our Engineer-to-Engineer (E2E™) forum
Recommended Parts
| Part Number | Automotive Qualified | VCC Range | Bits | Features |
|---|---|---|---|---|
| SN74HCS595 | 2 V to 6 V | 8 | Schmitt-trigger inputs,
3-State outputs Asynchronous clear input for internal registers | |
| SN74HCS595-Q1 | ✓ | |||
| SN74HC595B | 2 V to 6 V | 8 | X1QFN package (2.50 mm × 2.50 mm) |
For more devices, browse through the online parametric tool where you can sort by desired voltage, channel numbers, and other features.
