CYW92070xV3_EVAL evaluation board and Crystal Frequency

[Anonymous]

Hi,

CYW92070xV3_EVAL evaluation board hardware user guide says that pin BT_XTAL_STRAP_0 and BT_XTAL_STRAP_1 on CYW20706 or CYW20707 can be used to select XTAL frequency and it also says that the value of 1 on both BT_XTAL_STRAP_0 and BT_XTAL_STRAP_1 makes the CYW20706/07 to read the frequency from Non volatile memory.

Question :

Can you help me understand how to store XTAL frequency information into Non volatile memory ? When is this XTAL info read and applied ? How the XTAL freq used ?

It would be very helpful if you can direct to place in WICED SDK 5.0 where this is already being done.

Thank you,

Pravinkumar

[JacobT_81]

This configuration is done for you as part of the build process. It is controlled by the make target you use:

snip.bt.a2dp_sink-CYW920706WCDEVAL FREQ=40Mhz build

In earlier SDKs, there are separate platform files entirely:

a2dp_sink-BCM920706_P49_40MHz build

a2dp_sink-BCM920706_P49_24MHz build

Jacob

[Anonymous]

Got it, the SDK I am using has got separate platform files.

I am using CYW20706 and I would like to provide 18MHz crystall, Please help me understand ihow this configuration is written into non volatile memory and by the way I am not using the same flash memory as it is in eval board.

Please share with me a doc that explains this procedure completely.

Thank you

[JacobT_81]

We only support 20MHz, 24MHz, and 40MHz crystals for 20706.

Jacob

[Anonymous]

But, the 20706 data sheet says that it can support frequencies other than 20MHz, 24MHz, and 40MHz by firmware configuration (reading from serial flash or EEPROM).

--Pravin

[JacobT_81 · Accepted solution]

Correct, the chip is capable of other crystal frequencies ("19.2–52 MHz in 2 ppm steps"), however, we do no support these frequencies in WICED. You will need a custom FW config for this which will require dedicated support outside the scope of the forum.

Furthermore, we strongly advise using the xtal frequencies that we have tested on our side. Using 20, 24, or 40MHz is highly recommended.

Jacob

[Anonymous]

Hi, I have a question related to this issue. As I understand it, no matter 20, 24, or 40MHz is used, the chip will always run at 96MHz. The configuration file in IDE will handle it. Is that correct?

[Anonymous]

Yes, you are correct. The core will run off a 96 MHz  clock and the user need not worry about this. The internal circuitry will take care of this.

[Anonymous]

We've populated a 24 MHz crystal and roughly the correct load caps for the crystal (a pair of 15 pF caps for a crystal that expects 9 pF)  on our 20706 implementation. We've set the XTAL_STRAP lines correctly for a 24 MHz crystal.  I've verified with a nearfield probe that the crystal is oscillating at 24 MHz.

When we enter manufacturing test mode, and request a continuous transmission at 2.402 GHz, the tone is centered at 2.56708 GHz.  In my experience, this is too far out to correct with adjustments to the crystal load caps, so I would conclude that the manufacturing test mode expects a 20 MHz crystal, and ignores the XTAL_STRAP lines.

Is this correct?

[Anonymous]

I just confirmed that there is a problem with the ROM-based HCI code, in that it expects a 20 MHz crystal and ignores the bootstrap pins.   I replaced our 24 MHz crystal with a 20 MHz crystal and swapped the bootstrap xtal resistors accordingly.  Whereas the command "mbt set_tx_frequency_arm 1 2402 5 3 3" was formerly resulting in a 2.56708 tone, it now gives the proper tone at 2402 MHz.