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1-Wire Communication - Pull Up Resistor

Last Updated: June 13, 2011

Is an external pull up resistor required in 1-wire communication?


The Dallas Semiconductor 1-Wire® products are a family of devices that communicate over a single wire and a ground. The 1-Wire user modules of PSoC provide easy access to these devices.

A 1-Wire data line is an open-drain with a resistive pull up. This allows each device to 'release' the data line when the device is not transmitting so that the bus is available for use by the other devices.  So, the 1-wire bus requires an external Pull-Up resistor of approximately 4.7 kΩ.

However, it is also possible to build this resistor in the PSoC using PSoC's pin drives. The drive mode of the pin can be configured as resistive pull up using the PSoC's drive mode control registers, thus eliminating the use of external pull up resistor.

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