Editor's Choice


How to multiplex a 1-Wire host into multiple channels

30 August 2023 Editor's Choice DSP, Micros & Memory

1-Wire networks are designed for communication with a single 1-Wire host and numerous 1-Wire nodes on a single 1-Wire bus. Preferably, a linear topology, which contains insignificant stubs, is best for a 1-Wire network. However, a star topology, which contains long stubs, is often unavoidable, and makes it more difficult to determine the effective limitations. A method to eliminate these difficulties is to break up a star topology into numerous channels by using an analogue multiplexer (mux).

Advantages of using numerous channels include accelerating individual 1-Wire node access time, improving network robustness, and mixing overdrive-only nodes with standard/overdrive nodes on different channels. These advantages can be gained, while still having a single 1-Wire host.

Arrangement

When configuring a 1-Wire network to have many channels, the general approach taken uses an Analog Devices’ 1-Wire host connected to the common signal of an analogue mux. The mux has digital channel select signals to connect the 1-Wire common signal to the desired I/O that contains a channel of 1-Wire node devices. With this arrangement, many more 1-Wire nodes can be networked over the limitations of a single 1-Wire bus. This is due to the elimination of stubs, and a decrease in the number of 1-Wire nodes per channel driven by the 1-Wire host.

Examination

Figure 1 shows a 3,3 V system when using the DS2485 1-Wire host. The microcontroller controls both the DS2485 and the mux channel to be selected. In a 1-Wire network, it is critical that the mux used can handle rail-to-rail analogue signals. Otherwise, signal distortion can occur and the VPUP parameter requirement of the 1-Wire nodes can be violated. The mux RON parameter must also be as small as possible to avoid altering the DS2485 active pull-up impedance (RAPU). If this is not taken into account, the 1-Wire nodes might not receive the necessary current to operate during a strong pull-up event.

Figure 1. Typical application circuit.
Figure 1. Typical application circuit.

Optionally, the mux (U2) has external, post-mux, pull-up resistors (RP4 and RP5) to provide power for idle 1-Wire nodes when the switches are open. If this is not done, each time a channel switch is connected, the microcontroller must wait the maximum wake-up time of the connected nodes on that channel (usually 2 ms) before beginning communication. However, it is important to consider the effects of the mux’s RON parameter during a pulldown event by the 1-Wire host when using an external pull-up resistor on each channel. Any effects can be considered negligible by selecting a small RON to avoid violating the highest 1-Wire input low parameter of the 1-Wire nodes. So, for a given post-mux pull-up resistor of RP and a given mux resistor of RON, the post-mux output low voltage is expressed using equation 1:

Additionally, it is important to consider the flexibility of the 1-Wire host used. Analog Devices recommends the DS2485 1-Wire host for any 3,3 V system because the DS2485 timing, input triggering levels, and internal pull-up resistors are very adjustable. The DS2485 can also be set to a high impedance mode, which can be helpful when using the external resistor option. However, if a system needs 5 V, then the next best option is to use the DS2484.

Lastly, during this examination, some systems require a mix of overdrive-only and standard/overdrive 1-Wire node devices. If the overdrive-only and the standard/overdrive devices reside on the same 1-Wire bus, communication faults occur. One simple solution is to use a mux that places overdrive-only devices on different channels than the overdrive/standard devices. The DS2485 can then simply switch to overdrive mode or standard mode between the selection of channels for proper communication.

Analogue Mux Selection

There are many requirements a designer considers when selecting the analogue mux. These requirements can be the number of channels, interface type, cost, package type, and performance. Table 1 lists the recommended analogue muxes for 1-Wire applications. All the recommended analogue muxes handle rail-to-rail analogue signals, have a small RON, and come in various package types.

The microcontroller that controls the selected channel must have spare GPIO pins. If the microcontroller does not have any spare GPIO pins, it is possible to use the MAX14661 or a similar device that can be tied to the same I2C bus used by the DS2485.

Table 1. Analogue muxes for 1-Wire devices selector guide.
Table 1. Analogue muxes for 1-Wire devices selector guide.

Conclusion

This article provides a method to break up star topography 1-Wire networks by using an analogue mux from the recommended list. As with the selection of any electronic component, the supporting system should carefully examine all device specifications under all use conditions to ensure reliable operation.



Credit(s)



Share this article:
Share via emailShare via LinkedInPrint this page

Further reading:

Bringing Bluetooth Channel Sounding to automotive and beyond with KW47
Altron Arrow Telecoms, Datacoms, Wireless, IoT
NXP’s new Channel Sounding-certified KW47 and MCX W72 wireless MCUs are set to help automakers with distance measurement, bringing an additional ranging solution for car access and autonomous systems, and will be utilised across a broader spectrum of applications.

Read more...
What is Wi-Fi HaLow and why choose it for IoT?
iCorp Technologies Editor's Choice Telecoms, Datacoms, Wireless, IoT
Wi-Fi HaLow introduces a low power connectivity option that, in contrast to other Wi-Fi options, offers greater range of approximately 1 km, which opens up a raft of IoT use cases.

Read more...
Wi-Fi 6 and Bluetooth LE coprocessor module
Altron Arrow Telecoms, Datacoms, Wireless, IoT
The ST67W611M1 from STMicroelectronics boasts an all-in-one design which, together with its capabilities, contribute to making it an attractive choice for IoT edge devices requiring a single-chip solution.

Read more...
Wi-Fi 6 plus Bluetooth LE SoC
Altron Arrow Telecoms, Datacoms, Wireless, IoT
Silicon Labs’ SiWx917M SoC is the company’s lowest power Wi-Fi 6 SoC, ideal for ultra-low power IoT wireless devices using Wi-Fi, Bluetooth, Matter, and IP networking for secure cloud connectivity.

Read more...
Simple battery charger ICs for any chemistry
Altron Arrow Editor's Choice Power Electronics / Power Management
The LTC4162 is a highly integrated, high voltage multi-chemistry synchronous monolithic step-down battery charger and PowerPath manager with onboard telemetry functions and optional maximum power point tracking.

Read more...
Microchip enhances TrustMANAGER platform
Altron Arrow DSP, Micros & Memory
Firmware over-the-air updates and remote cryptographic key management provide scalable solutions for addressing IoT security challenges.

Read more...
Adaptive optics’ power solution
Altron Arrow Opto-Electronics
Vicor power-dense adaptive optical modules enable colossal telescopes to look into the past for deep space discoveries.

Read more...
Wide input voltage buck-boost converter
Altron Arrow Power Electronics / Power Management
The MAX77859 from Analog Devices is a high-efficiency, high-performance buck-boost converter targeted for systems requiring a wide input voltage range of between 2,5 and 22 V.

Read more...
From the editor's desk: Is the current AI really what we want?
Technews Publishing Editor's Choice
The companies that develop LLMs need to change direction and concentrate on freeing up our time, not so that we can have more time to do the tasks we don’t want to do in the first place, but rather to allow us more time to do what we love.

Read more...
High-density power module for AI at the edge applications
Altron Arrow Power Electronics / Power Management
The MCPF1412 power module from Microchip has integrated I2C and PMBus interfaces for flexible configuration and monitoring.

Read more...









While every effort has been made to ensure the accuracy of the information contained herein, the publisher and its agents cannot be held responsible for any errors contained, or any loss incurred as a result. Articles published do not necessarily reflect the views of the publishers. The editor reserves the right to alter or cut copy. Articles submitted are deemed to have been cleared for publication. Advertisements and company contact details are published as provided by the advertiser. Technews Publishing (Pty) Ltd cannot be held responsible for the accuracy or veracity of supplied material.




© Technews Publishing (Pty) Ltd | All Rights Reserved