Disconnect the MCU from the TRF7970A

Thank you.

EN must be 1 to enable the TRF7970A for inputs. Is this right? Otherwiese the TRF7970a is sleep mode.

I don't understand this sentence: "If EN2 is connected to VIN, then VDD_X is active during power down mode 2 (for example, to supply the MCU)."

Why should the MCU be supplied when the TRF7970 is in power down mode?

The next question is when do I need this 60 kHz clock? "If EN = 0 and EN2 = 1, then system clock is set to 60 kHz"

Thank you alot, best regards, Flo

Hi,

Of course buying one new booster pack is the best choice in this case, no doubt about it, but in some cases people prefer to modify the EVM instead of buying new hardware. In fact we also did it that way and suceeded at the end.

What I don't agree with is removing the MSP430 MCU from the board as it is not required and makes impossible to revert the changes.

The EVM design presents one little inconvinient, you can not completely isolate the TRF7970A from the MCU as some signals (like DATA_CLK) are directly connected between both chips, with no resistor in the middle, and some others are not connected to connector headers (like EN) and must be wirewrapped. But all that can be solved with two simple wires, one for wiring EN to one free pin in one of the headers and the other for forcing low the MSP430 reset pin (that way it avoids having to cut any PCB route).

Regards,

--Victor

Hi Flo,

The regulator output VDD_x can be used to power some other external devices, like one low power MCU. The sentence "If EN2 is connected to VIN, then VDD_X is active during power down mode 2 (for example, to supply the MCU)" means exactly what it says, VDD_x will be active even if EN is disabled (powerdown mode) and you will be able to use it to power some external electronics. But be careful as VDD_x output value is internally adjustable.

Powering or not the MCU while the TRF7970A is in sleep mode is always up to your design needs. If your device is battery powered and only listens and reacts to RF field events, it could make sense to put it into sleep mode or even power it down, but things are different if you need to check some other signals (touch sensor, switch, USB, etc). If you decide to power down your MCU take into account the time it takes to boot up as it could prevent you from responding in-time to RF field events.

Low frequency clocks (as 64KHz) are usually used to make the MCU work at the lowest power consumption as possible when it has nothing else to do but making some very simple checks (e.g. IO pin reads) that require just a few clock cycles to complete. In the case of the TRF7970A this is handy as you can use the same 13.56MHz crystal for clocking the TRF7970A and the MCU, once again, it is up to your application if this feature is useful for you or not.

For most applications the MCU is externally powered, not powered from VDD_x, and has its own oscillator or resonator crystal so you will not have to worry about those two signals.

Regarding the modifications of the EVM, please take a look into the first part of this post (TRF7970A SPI Operation Issue, not responding to reads) as the modifications we made and worked well are listed there. The communication problems described there are already solved and were related to SPI master controller configuration settings.

Hope it helps you,

--Victor

Yes it helped a lot. Thank you.

In your other post you said: "Grounded the MSP430 RST Pin (pin 38) so it's always under reset conditions and doesn't start writing pulses to DATA_CLK."

Is it now possible to use my on DATA_CLK and connect it to HDR_1 DATA_CLK without cutting the conducting track?

Do you know it is possible to use my own antennas with the TRF7970A Booster Pack?

Best regards

Flo

Hi Flo,

Yes, the idea on keeping the MCU under reset condition is make it keep the out pins in Hi-Z state so it is possible to connect them directly to external hardware (feeding the DATA_CLK from your external MCU).

In theory, the booster pack supports connecting one external antenna. The datasheet can be downloaded here: dlp-7970abp-ds-v11.pdf.

You may also connect one external antenna to the EVM, but we did not try it.

--Victor

Thanks alot for your help :)

Best regards

Flo

Victor,

Thanks for chiming in with your experience here!

Flo,

You can use an external antenna with the DLP-7970A Boosterpack.  To remove the on board antenna, you should remove C23 and C24.  CN1 allows for adding a u.fl connector where you can connect your 50 ohm matched antenna.