Table of contents

RoadTest: Enroll to Review the Renesas Solution Starter Kit for RX23E-A

Author: Jan Cumps

Creation date: 5 Jul 2023

Evaluation Type: Development Boards & Tools

Did you receive all parts the manufacturer stated would be included in the package?: True

What other parts do you consider comparable to this product?: I didn't find microcontrollers with a comparable set of analogue capabilities

What were the biggest problems encountered?: The first steps. A simple step guide to complete the first successful exercise.

Detailed Review:

Review Goals

I focus on the Out of Box experience. This is the request from the organisers:

”Working with the documentation, and testing the out of the box experience. Show us what you discovered through text, images, videos, and/or any other media, so the reader understands what is involved in using the product.“

At the end of the review you’ll find a link to a set of elaborate posts that go beyond this goal, and review aspects of this kit in detail – with examples.

What is the Starter Kit and RX23E-A microcontroller

The kit is a combination of an evaluation board, a PC application, and a set of documents, examples and firmwares to help you review the controller’s capabilities. Focus is on the RX23E-A’s analogue performance. It comes with a K-type thermocouple to allow you to test a concrete scenario.
The evaluation board has 5 main components:

• the controller
• access to controller’s ADC inputs, analogue front end and supporting signals
• power section
• USB serial interface
• thermocouple example circuit

The RX23E-A is part of Renesas’ proprietary RX core family. this part is the one specialised in digitising analogue signals. Its processing power and digital capabilities sit at the low side of the family hierarchy. For the analogue capacities, it’s the very top one in the RX series.
It has 2 analogue channels, each with

• 8x1 input multiplexer
• programmable amplifier
• buffers
• Delta-Sigma 24 bits ADC
• configurable digital-side filter

related utilities:

• voltage references and bias outputs
• current sources
• DMA and interrupts

Getting Started

The starter kit arrives programmed with firmware. In combination with a Windows application called PC Tool, you have the setup to start evaluating a generic ADC scenario right away. You will need to read the kit’s documentation though. Plugging in the kit and trying to achieve something meaningful with the PC Tool will not get you anywhere. This is the right point to 

• read the Starter Kit Quick Start Guide to select a good power option,
• read the PC Tool User Guide to understand what it does and how you interact
• read the first part of the Starter Kit User’s Manual, ending with 2.4.2 DSAD Measurement Circuit.

This is my first critique for this Starter package. This is only obvious after you’ve done it. It’s missing a single page step-by-step guide to get a first measurement or waveform on the PC screen. I’m going to fix that in the next section, with a “get up and running in 10 minutes” guide.

Generic ADC example: Measure a 1.5 V battery

This is my simplification of Renesas' out-of-box DSAD example. I reduced it to a number of repeatable steps without the need of piecing together parts from different documents.
you need:

• the kit
• USB cable
• PC Tool software
• Windows computer
• 1.5 V battery
• 2 wires, preferably a red and a black one

Steps

• Install the PC Tool
• Configure USB as the power source:
  • set JP14 to Vbus (pin 5 and 6), this is NOT the default out of box setting
  • set JP15 to VCC (pin 2 and 3), default
• Configure ADC inputs:
  • set JP11 to pin 1and 2 + pin 3 and 4, default
  • set JP12 to pin 1 and 2, default
  • Leave other jumpers where ever they sit
• Prepare the battery:
  • fix red wire to +, black wire to –. You can use tape, or push the battery in a holder with the wires stuck between battery and contacts.
  • Don’t connect to the board. There should be no signal if the controller isn’t powered up.
• Connect the board to the laptop:
  • Start Windows Device manager, and click on the Ports node.
    Take note of any existing COM ports
  • Use the provided USB cable to connect the board with your PC
    A new COM port will appear. Write it down.
  • Start the PC Tool
    Go to Settings → Configure
    Select the new port, leave the BaudRate
    In the WaveForm tab, click Run
    Note the waveform, and the values of MAX, MIN, MEAN
• Connect the battery:
  • Connect the black wire (minus) to AIN2, CN2, 6th position from top
  • Connect the red wire (plus) to AIN3, CN2, 7th position from top

Note the waveform, and the values of MAX, MIN, MEAN again.
Use MEAN to check if the input value is 1,5 V, using this formula:

I did the same exercise. Only difference: I used a voltage reference instead of a 1.5 V battery. The reference is measuring 2.49978 V on a Keithley DMM6500. The Starter Kit reports 2.498176 V. According to the PC Tool, my setup achieved 16 effective number of bits.

Once you followed the steps above to get your first experience with the kit, it ‘ll be easier to start reading the PC Tool User Guide and the Starter Kit User’s Manual. You now have the context, and understand what it’ll lead to.

Variations on the Generic ADC example

• Use different input signals (sinus, …), mind the lower and upper voltage limits
• Use a better source for the digital and analogue power sources. The USB voltage is OK for first run, but not to operate at high precision.
• Apply a signal to the second channel too (AIN8 is low, AIN9 is high)
• Play with amplifier gain
• Play with waveform and histogram tab settings to get good views

Real world example: Thermocouple with 4-wire RDC cold junction compensation

This is the highlight of the evaluation kit. A real good setup to measure the low-level signal of a K-type thermocouple.
Only using the RX23E-A analogue options to condition the signals for optimal sampling. There are no external signal preprocessors.

• It provides bias voltage for the thermocouple and reference voltage for its ADC
• The programmable gain amplifiers raise the analogue signals before sampling. And
• one of its current sources supplies the excitation current for both the cold junction compensation RDC and its reference voltage.
• The digital filter is used after sampling, to filter out 50/60 Hz noise.

This example is documented in application note R01AN4747EJ0110: Temperature Measurement Example Using a Thermocouple. A very good document that describes the design, and all configurations and algorithms for the design. The Starter Kit has the K-type thermocouple needed to run this example.

The firmware to run this example is not available as a download is. Renesas published the e2 studio project with sources, so generating the binary firmware isn’t difficult. Yet it involves some configuration - see this blog post. Alternatively, you can download the archive at the end of that blog post. I included a precompiled binary in that .zip.

When the firmware is loaded to the board, and you start the PC Tools, the Application tab becomes active. The application starts logging the temperature

Variations on the Thermocouple example

After finishing that exercise, I used the PC Tool to save the register settings to a configuration file. That allows me to use the standard PC Tools functionality, with the RX32E-A front end configured exactly as in that example.

You can find that file as an archive at the end of  Renesas Solution Starter Kit for RX23E-A: register configuration for the Thermocouple app note .

Is there more?

Yes. 

• There’s an example for a strain gauge. Also very elaborate, with its own application note and source code.
• And lots of combinations with front-end, ADC and digital filter to play with.
• And – if you have a debugger – the option to play with the code, learn efficient sampling, learn how to maintain a tight loop…

Why didn’t I elaborate on precision, on specs?

The ask for this Road Test was to evaluate getting started with the Starter Kit. I’ve done the more detailed exercises. They are in separate blog posts. links at the end.

Conclusion

The RX32E-A is a unique controller. Unique for its pair of 24 bits ADCs and the analogue front end options.
It’s capable to drive and read low signal analogue sensors, or read inputs with a very decent accuracy and precision.
The analogue front end and utility signals are flexible and will work for some of the complexer setups.
If the signal fals inside the allowed input voltage window, you may not need additional analogue circuitry.

The Starter Kit manages to show that, and to help you evaluate both the prepared examples, and your own specific needs.
You can change front-end, ADC, utility and filter settings on the go and start sampling.
The addition of that well-designed “K-type Thermocouple with compensation" circuit is a good choice. This is one of the often used - not always well executed scenarios that many engineers have experience with.

The documentation, as usual with Renesas, is very complete and detailed. At the same time, it’s also somewhat difficult to read and follow (again as usual for Renesas).
If they add a “get started in a few minutes, learn later” leaflet, it would be ideal.

For the engineer that needs to evaluate the controller, this kit is a great tool.
For the electronics enthousiast that wants to learn some pro approaches to precision ADC, this kit and the documentation are packed with knowledge. You can test and compare theory with reality right away.

Now it’s time for the real review. A set of posts that review hardware, software, examples, specifications.
Enjoy: