Part 1 of this blog series reviews the wM-Bus protocol standard in the European 868MHz ISM band, while Part 2 looks at the wM-Bus N mode and ETSI Class 1 specification receiver performance. Now, let's take a look at how the wM-Bus subsystem, embedded solution or independent RF module in the actual use environment is designed, and what the next generation solution looks like.
When designing a wM-Bus solution, whether you are implementing the wM-Bus module or the embedded RF subsystem, you must first determine the operating location of the wM-Bus stack. This device can be a master metric microcontroller (MCU) or a separate MCU dedicated to the operation of the protocol stack. The advantages of combining the RF protocol stack with metrics on the same MCU include:
Reduced PCB size
Maximize existing flash, RAM, and other MCU resources
Reduced costs compared to 2 MCU solutions (1 for metrics and one for stacks) (most of the time)
However, this single MCU approach also has some drawbacks:
The authentication of the metric component, along with the communication protocol stack, may cause firmware changes (related to RF or metrics) in the future, which requires re-authentication of the entire system.
Both metrics and RF communication are time-critical tasks. This can be a real problem when using MIPS-limited ultra-low-power MCUs (for example, 2-3ms in T2 mode for "other" devices). Response time)
Cost reduction options and/or higher performance upgrade options for MCUs and RF devices may be limited, and in general, with separate MCUs and RFs provides much greater flexibility and is easily available from pin-compatible devices. Find the best device for each task
Regardless of whether 1 or 2 MCUs are used, the wM-Bus subsystem will require an MCU for the stack (and possibly for application and/or metric code), as well as an RF device, with their respective wMs. -Bus mode compatible. TI is offering a wide range of ultra-low-power MSP430TM MCU devices with FRAM MCUs that run the wM-Bus stack when combined with the high-performance CC112x family of RF devices. On the other hand, a large number of device combinations (hundreds of MCUs and six RF devices) make the necessary stack adjustments for each option. Each time a new solution is designed, different SPI interfaces, changing reset and interrupt lines, and GPIO connections between the MCU and RF must be considered, which greatly increases the design effort.
In wM-Bus mode, the introduced SimpleLinkTM Sub-1 GHz CC1310 wireless MCU guarantees RF performance without any hardware changes. Three different QFN packages (4x4, 5x5 and 7x7 mm) enable a wide range of applications based on the number of GPIOs required by the user's application, such as heat metering, water and heat meters, and RF modules. For a wM-Bus RF subsystem (both instrument and data collector functions), with just one UART connection and several other lines, the 4x4 package is the right size and can be implemented in a true single-chip wM-Bus system or RF Module. A single integrated passive component (IPC) already available for CC112x (see here) will make this CC1310-based solution even more attractive and enable smaller wM-Bus compatible modules in the 433 and 868 MHz bands .
Is the Sub-1 GHz CC1310 a better wM-Bus solution than the CC112x series?
Neither is it, depending on the required wM-Bus mode and device functionality, and which parameters are most important for a particular product.
Figure 1. Comparison of wM-Bus mode between CC112x/CC120x and CC1310 series
As shown in Figure 1, the CC1310 wireless MCU operates in the 433 and 868 MHz bands; therefore, S, T, C, and F modes can be supported. Only the CC1120, CC1200 or CC1125 intelligent RF transceivers support narrowband N mode in the 169MHz band.
For the 868MHz band, RX sensitivity and blocking are similar performance, however, due to the efficacy characteristics, CC1310 performs well in terms of current consumption. When powered by a 3.6V supply, the current drawn in receive mode is only 5.4mA, and the current in transmit mode is 22.5 mA @ +14 dBm (conducted measurement). Compared to the CC112x series, the total power consumption of the CC1310 in receive mode. (Voltage U multiplied by current I, the voltage remains the same) is reduced by 75%, and the power consumption during the emission operation is reduced by half. The drastic reduction in energy consumption makes it possible to use small size batteries and low cost snubber capacitors, thereby reducing system cost.
The third very important mode of operation (in addition to receiving and transmitting) is a sleep or power-down mode with a real-time clock, including full RAM state retention—where the current consumption is only 650nA, which can be compared to many CC112x/CC120x radios. The ultra-low-power MSP430 device family is comparable in its combined sleep current in power-down mode.
With up to 128KB of flash memory and 20KB of RAM, there is plenty of memory in a single device to combine the wM-Bus stack with the application code. Because of its market-leading ultra-low power consumption, along with excellent receiver sensitivity, selectivity and blocking performance, the new CC1310 wireless MCU is ideal for a wide range of applications and products, such as water meters or heat meters, heat distribution meters, and consumption. Class display products, as well as wM-Bus RF adapters, are endless.
The last blog in this series will talk about power solutions for Sub-1 GHz RF systems, don't go away, Part 4 is coming right away.
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