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  • Author Author: Jan Cumps
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Renesas Solution Starter Kit for RX23E-A - break out the SPI signals

Jan Cumps

I'm about to design some analogue measurement devices based on the Renesas RX23E-A controller. With SPI as communication channel between that IC and a more generic communication/processing board.

The full design of the future project is still settling. Most likely it 'll have the RX23 do the analogue duties. Another controller (or SOB?) doing the data handling and communication. Isolation between the two for power and communication. What I want to try now, is to set up a decent RX23 architecture. Hardware and software. At this time: can I create firmware that uses the RX23 to do high fidelity sampling, and exchange data via SPI (act as a SPI client).

I have an evaluation board from Road test: Renesas Solution Starter Kit for RX23E-A. It has options for USB, CAN and RS-485/profibus. Out of box, it doesn't expose SPI. But it has the capabilities to do so. This blog shows a few modifications I did to get at the SPI signals.

The application note for this kit shows what I can get at without needing bodge wires. The connector J3 exposes a number of communication lines. Including ones needed to use the SPI peripheral. But several of them are connected to the SPI and profibus ICs. So i need to do a few little changes.

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I've been checking all options for the SPI signals:

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and here's what I selected:

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On the PCB, I need to mount J3, and remove R90 and R28. The resistors are 0402 and 0603. Doable when careful.

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Before:
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After:

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Not so difficult with this kit. The two resistors have enough space to work on them. I used a decent flat solder tip and shoved them off their pads. J3 is a standard pin header. Easy to solder, if you use enough power for the pins that are connected to the power planes. I taped the resistors on a piece of paper and put them inside the kit's box. In case I want to restore it to its original configuration.

All set to start checking if I can write decent firmware ...

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