The bus can be overdriven to a maximum data speed of 125 kbps.
This is a low-speed serial communication standard, with a typical data speed of 15.4 kbps. Every master device is identified by a 64-bit address, stored within each one-wire slave device’s ROM. What they can do is indicate their presence over the bus when the master resets. The master device is solely responsible for the read and write operations of the slave devices, so they cannot initiate a data transfer on their own. Instead, the slave devices are internally clocked and synchronized with a signal from the master device. This protocol does not use a clock signal. However, as slave devices are added to the bus, their polling by the master device might take more time. It’s possible to connect up to 100-slave, 1-wire devices, with a 1-wire standard bus. An additional wire might be necessary, depending on the power mode.Ī 1-wire standard has a master and slave configuration, where there can only be one master device, a computer or microcontroller, and several slave devices. Although this protocol is classified as a 1-wire standard, at least two wires are required in the 1-wire standard bus - one for the data and/or power supply and another for the ground return. The PIO pin is off by default, so Q2 is included for convenience and safety.The 1-Wire protocol is a single-wire interface, half-duplex, bidirectional, low-speed and power, long-distance serial-data communication protocol. Diode D1 limits the PIO-pin voltage to a safe level, and transistor Q2 provides an additional logic inversion that makes the state of the DS2405 internal pull-down correspond to the state of the load. R1 and R2 form a voltage divider that provides an adequate signal swing at the PIO pin. However, the state of the load cannot be read because Q1's base-emitter voltage limits the voltage swing at the PIO pin. Q1 acts as an open-collector switch connected to the load. 2 may be more practical and cost effective. On the other hand, a discrete-component circuit such as Fig. Or, designers can use a relay for loads that exceed switch ratings, especially for applications that feature high current or high voltages such as 120 Vac ( Fig. Other devices with higher ratings can solve the problem for some applications.
The PIO pin of that device is limited to 6 V or 4 mA, which restricts the type of load or relay it can drive. By monitoring voltage at its PIO pin, the DS2405 also lets designers read back the state of the load. The load can be connected to the open-drain switch directly, or indirectly through a relay. One-wire switches such as the DS2405 from Maxim Integrated Products allow designers to control remote loads through the versatile one-wire network.
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