1-Wire - How long can a 1-wire bus be
1-Wire communication protocol, known for its simplicity and robustness, enables data transmission over a single wire. However, the length of a 1-Wire bus, crucial for network reliability, is determined by its capacitance. When capacitance exceeds a certain threshold, the signal propagation becomes sluggish, hindering effective data transmission.
In the realm of 1-Wire communication, the maximum allowable capacitance for the bus is set at 10 nanofarads (nf) or equivalently, 10,000 picofarads (pf). This threshold ensures that signal transitions occur swiftly enough to sustain accurate data exchange. Various types of cables and connections introduce different levels of capacitance into the bus.For instance, twisted pair Cat5 cables, commonly utilized in networking setups, typically exhibit a capacitance of approximately 50 pF per meter. On the other hand, flat phone cables, often found in household telephone installations, boast a typical capacitance of around 60 pF per meter. Meanwhile, printed circuit board (PCB) traces, employed for on-board connections, typically contribute about 24 pF per meter to the bus's capacitance.
Moreover, each additional 1-Wire slave device connected to the bus imposes an extra 30 pF of capacitance. This cumulative effect must be considered when calculating the maximum permissible bus length.
To illustrate this concept with an example: Suppose a 1-Wire bus supports 20 devices and utilizes phone cable. To determine its maximum length, the formula [(10,000 pf - (20 devices * (30pf / device)))] / (60pf / meter) is employed. Substituting the values, we find that the maximum allowable length for this particular configuration is approximately 156.67 meters. Understanding the relationship between capacitance and bus length is imperative for designing robust and reliable 1-Wire networks. By adhering to capacitance limits and considering the cumulative effect of connected devices, engineers can ensure optimal performance and data integrity in 1-Wire communication systems.