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1 Wire Cables, connectors and pinouts
This page summarizes the factors behind choice of cabling, connectors and pinouts for connecting 1-Wire Master and slave nodes as well as network topology.
1-Wire networks kan work with almost any cables and topology (bus, star, bus+stubs) as long as the overall cable length is short (a few meters). For longer networks, running tens or even hundreds of meters, you need to take many factors into account before deciding on topology, cabling and termination. As a general rule, you should avoid star topology, and stick to a basic bus topology, or a bus with nodes located off short stubs. Use Category 5 (or higher) cabling – the same you typically use for ethernet – and use the right cable cores (twisted pairs), for the right 1-Wire signals and power. Doing that, you can be fairly certain to minimize bus/network errors.
At References section of this page, I have included links to valuable resources on 1-Wire network topology, cabling, termination (connectors and pinouts) and drivers.
For limited network sizes with a total cable length up to 20 meters, telephone wiring (typically using twisted pair, solid core, permanent wiring and flat, parallel multi-core connection cables with RJ12 (6P6C: 6 position, 6 connection) or RJ11 (6P4C: 6 position, 4 connection) connectors can be used.
The proposed pinout for the RJ12/RJ11 connector is:
| RJ Pin | 1 | 2 | 3 | 4 | 5 | 6 |
|---|---|---|---|---|---|---|
| IDC cable color | white | black | red | green | yellow | blue |
| Twisted cable pairs | 3 | 2 | 1 | 1 | 2 | 3 |
| RJ12 | Regulated +5VDC, <50MA | Power Return (Ground) | One Wire Data (OWIO) | One Wire Return (OWRTN) | NC | Unregulated +Supply <500ma |
| RJ11 | NC *1 | Power Return (Ground) | One Wire Data (OWIO) | One Wire Return (OWRTN) | NC | NC *1 |
- *1 Pins 1 and 6 are NOT available (connected) in RJ11 connectors and -wiring
- NC: Not Connected
- Source: DALLAS ONE-WIRE RJ11/12/14 CONNECTOR STANDARD
It is evident from the above standard, that RJ11 connectors and/or wiring, with only 4 connected wires, can only be used for networks exclusively populated with parasitic powered 1-Wire slave nodes.
The only current 1-Wire offering from Maxim (formerly Dallas) using an RJ11/RJ12 connector is the DS9490R USB to 1-Wire Adapter. The pinout of the RJ12 socket (mislabelled as RJ11), is:
| RJ12 Pin | 1 | 2 | 3 | 4 | 5 | 6 |
|---|---|---|---|---|---|---|
| Signal Name | VDD | GND | OW | GND_OW | SUSO | N.C. |
| Description | 5VDC Output | Power Ground | 1-Wire Data | 1-Wire Return | USB Suspend Output | No Connection |
A similar pinout (without the SUSO signal) is used by DS2484 I2C to 1-Channel OneWire Master Breakout.
The proposed pinout for the RJ45 connector is:
| RJ45 Pin | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
|---|---|---|---|---|---|---|---|---|
| TIA/EIA-568 T568B cable color | orange/ white | orange | green/ white | blue | blue/ white | green | brown/ white | brown |
| Cable pairs | 2 | 2 | 3 | 1 | 1 | 3 | 4 | 4 |
| Signal | Regulated Power Return (Ground) | Regulated +5VDC (<50MA) | NC | One Wire Data | One Wire Return | NC | +12VDC (<200ma) | 12V Return (GND) |
| ID | PWR_RTN | PWR_VCC | - | OWIO | OWRTN | - | VRAW | VRAW_RTN |
| Status | Opt 1 | Opt 1 | - | Mand | Mand | - | Opt 2 | Opt 2 |
- NC: Not Connected
- Source: A Guide to the 1WRJ45 Standard
The only situation where cross-plugging Ethernet and 1-Wire poses a risk to either circuit would be if the Ethernet is providing PoE (typically used in CCTV), and even then, this risk is theoretical, when using standards compliant hardware
For regular Ethernet (10BASE-T, 100BASE-T, 1000BASE-T), damage the 1-Wire nodes is extremely due to the Ethernet signal levels. Any low level currents generated by ethernet signals, when applied to 1-Wire signals, even with reverse polarity, will be easily handled by the ESD protection circuits of the driver circuit. Damage to the Ethernet nodes is also extremely unlikely, due to the DC shielding used in Ethernet signal interfaces, combined with the DC tolerance of PoE PDs (Powered Devices).
For Ethernet with PoE, there is a theoretical risk of causing damage to the connected 1-wire nodes, which only occurs, if one of the following unlikely situations exist:
- The 1-Wire interface exhibits a 25kΩ resistance between pins 1-2, 3-6, 4-5 or 7-8, which is sensed by the PoE PSE (Power Sourcing Equipment) before switching on power. This is extremely unlikely to be the case, and can easily be prevented by design/pinout.
- The PoE PSE does not conform to the PoE standard (IEEE 802.3af/at), in which case all bets are off. But to my knowledge, this is also very unlikely to happen.
The benefits to using RJ45 and associated Ethernet cabling (CAT5e, CAT6) are many, however.
- Ethernet cabling conforms to strict standards with regards to resistance, capacitance and inductance, making it a more predictable choice.
- RJ45 connectors, Ethernet cables and RJ45 patch cables are ubiquitous, and their cost comparable favirably with RJ11/12 connectors and cables.
- Most modern office and industrial buildings are pre-wired with RJ45 wall sockets connected with CATx compliant cabling, which terminate at patch panels or switches. This cabling can be easily used for 1-Wire devices using RJ45 connectors. RJ11/12 connectors could also use such existing wiring, but would require RJ45-to-RJ11/12 adapters at both ends.