PN7462 has an Integrated contact interface which supports Class A, B, and C cards with a Clock generation up to 13.56 MHz. Normally we use the default system clock of 27.12 MHz as the CT's reference clock, by which we may have 13.56 MHz, 9.04 MHz, 6.78 MHz, 5.42 MHz, 4.52 MHz, etc for the ISO7816 clock out frequency.
Alternatively there is another refence clock available for this module : the 48MHz USB clock as shown on page 78 of https://www.nxp.com/docs/en/user-guide/UM10858.pdf , which provides more possibilities for the ICC clock configuration.
Users may verify this based on the demo of PN7462AU_ex_phExCT7816_mcux from NFC reader library for PN7462 version 6.11 or above.
The configuration may be easily achieved with the following steps:
1.add USB PLL clock initialization in the main().
2.comment out CT initialization called in phFlashBoot_Main() as it is recommended to get USB clock source ready before CT initialization, and since the CT gets initialized in main() as well in this demo , so no warry about it.
3. update parameters to generate BaudRate for the cases of TA1 = 0x1x. (so far I just updated the cases for TA1 = 0x1x, I will address more on how to extend the configuration for more cases later .)
As you see, some cases could not have a 4.8MHz , that is due to Di parameter from the TA1 byte. I will let you know how to configure the parameters later.
With above modification , I have managed to drive a 4.8MHz clk out of PN7462, please kindly refer to the following for details.
The test result is shown as below:
Since I just used a Mifare SAM AV3 card in the test, the demo could not go to the end, but at least it shows the communication has no issue.
You may just directly replace several files in that demo with the same files as attached to verify it from your side.
To extend the definition of the configuration table above, please refer to the following for details.
With such configuration, there is no problem to have an ICC clock between 4.7MHz and 5MHz.
