How to port the ST25RU3993 firmware to a stand alone MCU board?

[MSerr.1]

Hi there,

We are working with the ST245RU3993 and have the EVAL board working correctly with the provided GUI.

We now want to control the ST25RU3993 via SPI with a ARM MCU. This ARM MCU will operate independently, as sketched in "Device side usage" in the STUHFL User Manual (see attached file).

Is there any guideline to follow on how to achieve this setup? Or any indications, hints or tips?

So, our aim is to have an independent MCU that controls the ST25RU3993 to read/write to the tags in range.

Thanks in advance,

Max Serra

[LKUMA.1]

Thanks Nick for confirming.

IN principle, this would imply removing R13, wire-grounding the EN in J12 and making a direct wired connection from the MCU (Pin 43) to EN on our custom PCB.

So no change needed in the FW/GUI.

1.) Additionally i would like to clarify if the on-board carrier cancellation and its, tuning process in the GUI/FW will have an impact on our reading process ? I could disable the tuning process in the GUI while External PA and Antenna select would still be running in the background. Is this correct ?

2.) What about using J11 UART LOG to enable the external RFID chip. We would still need to change the FW MCU to disable the on-board RFID Chip but the FW on the HOSt side (GUI) can remain unmodified ? would this still work or you consider this further efforts in FW development.

best ansd thanks for the recommendations.

LK

[Nick K]

Hi LK,

yes with removing R13 this should work.

ad 1) If you do not execute either tuning, pre-tuning or auto-tuning in the GUI no tuning is done. Meaning, when you not press the tuning button and untick the Pre-Tuning and the Autotuning checkboxes no tuning is done during scanning, also not implicit.

On the EVAL board the tuning process is simplified spoken finding the best values for the 3 tunable caps U6, U7 and U8. This is done with reflected power measured with the ST25RU3993. This means in your case you read the reflected power then at your new RF-frontend and the FW will then try to change the tuning caps on the EVAL board, which does not have any effect. The tuning then in the GUI is useless and will show wrong results. If done during scanning with autotuning it just waste time without any effect.

ad 2) Sure, the TX pin of the LOG UART can be reused if you do not need it for logging. The FW just use it to log out info if someone wants to instrument the FW. Adding log instruction to the FW code. If you do not want to log anything you can use the pin for other purposes, but this would mean that you have to re-build the FW to reconfigure the pin and to set or reset it when needed. The GUI is not using this LOG UART at all.

BR Nick

[SPhun.1]

Hello Nick,

I also want to drive the ST25RU3993 chip with a different MCU but I am using the HPEV eval board.

Do the steps described also apply to the HPEV board?

Are there additional modifications to be done? (For example, do I need to connect the PA_LDO_EN to my MCU? And what about the antenna selection?)

Finally, for the HPEV eval board power supply, are the 800mA @ 5V still applicable?

Thank you.

Best regards,

Stéphanie

[Nick K]

Hello,

yes,

steps 1 (remove R7-13) and step 2 (remove R61, short C25) are the same for EVAL and the HPEV board.

For step 3: The HPEV board uses three tunable capacitors, accessible via a RFFE interface, to establish a carrier cancellation system. Remove R38-40 to disconnect them from the on-board STM32L4 MCU. To control them use the pins ETC1-3 at J13.

For step 4: Also the HPEV has an RF switch to switch between antenna port 1 and 2. To disconnect remove R92 & R93 and control them then via the pins ANT_V1 and ANT_V2 at J31.

In addition you should control the external PA supply enable line. To disconnect from the onboard MCU remove R43. And to control it use the pin PA_LDO_EN at J4.

For the power supply, yes 800mA @ 5V should work, but is marginal when using the PA. Its recommended to use a power supply with 5V and 6W. As the one that is added to the HPEV board, to be on the safe side.

BR

Nick

[SPhun.1]

Hi Nick,

Thanks for the reply.

Based on your answer on the power supply, shall we understand that the board needs to be supplied via P2 with 5V@1.2A?

We are thinking of only using the external PA from the evaluation board so we understand that we also need to provide 6V to the board. Is there a way to provide those 6V besides using the power adaptator provided with the HPEV board kit?

Also, we have seen on the schematic the Plug_Enable controlled by the STM MCU. What is its use and should it be controlled by the external MCU? 

Finally, on our MCU side, we do not have enough GPIO output to control all required pins. Is it an issue if, instead of controlling the EN and PA_LDO_EN by the MCU, we force to HIGH the EN and PA_LDO_EN pins (Hardwired)?

Best regards,

Stéphanie

[Nick K]

Hi Stéphanie,

On the HPEV board the USB (P1) must be plugged to supply the board in general.

And for the PA either (recommended) use the power adapter from the HPEV package via J14 (power jack)  or if you do not want to use this you can supply the PA direct via J21 with 5V on the VPA pin. But as this direct supply the PA this must be a stable supply (no switching power supply) for proper operation of the PA. 

For the Plug_Enable pin. This is actual not used on the HPEV board FW. The board has the connection if someone wants to control the plug, but its not used in the FW.

For the PA_LDO_EN pin. Please do not hardwire this pin as this would mean that the PA is enabled even if no input signals are provided.

If you want to save GPIO pins there are two other/better options, that could save GPIO pins.

1. If you do not need to use the internal PA you can hardwire the PA switch and force the usage of the External PA. This can be done with the pins PA_V1 and PA_V2 (J30)

2. If you do not need two antennas you could hardwire the antenna switch to use only antenna 1 with the antenna switch pins ANT_V1 and ANT_V2 (J31)

BR

Nick

[SPhun.1]

Hello Nick,

Let me summarize the recommendations around the HPEV board power supply:

• Supply the board via P2 with 5V@1.2A
• AND supply the use of the external PA via VPA pin of J21 with 5V

Is that correct?

About the saving of GPIO pins, in fact, we have already planned to hardwire the PA and the antenna switches.

We only have 3 spare output GPIOs and we were thinking of using them to control the 3 ETC_x.

From our understanding, the remaining pins that need to be controlled by the MCU are the EN pin and the PA_LDO_EN pin.

1) Is there other pins that need to be controlled?

2) Is it possible to hardwire the EN pin (Which means that the RFID chip is never powered down)?

3) Can you detail what is the impact of having the PA enabled while no input signals are provided?

Thank you for your help.

Best regards,

Stéphanie

[Nick K]

Hello Stéphanie,

Regarding the power supply.

In general correct, but at P2 5V@100mA is enough. A standard USB cable/connection is sufficient as supply. And for the PA supply with 5V at VPA there you need the 1.2A

Regarding the other questions

ad 1) no

ad 2) yes possible

ad 3) on the HPEV board the PA gets very hot if always enabled. There is a thermal issue with the IC then on the board.

BR

Nick