Charger Detect registers

[vix]

I work on a SOM from Toradex, based on VF61 SoC.

I'm trying to investigate the built in charger detection mechanism in the Vybrid SoC, so I downloaded the reference manual (VFXXXRM Rev. 0, 10/2016)

I did some tests, both with a dedicated wall charger and with a host charger, but I can't understand completely how registers USB_ANALOG_USB0_CHRG_DETECT and USB_ANALOG_USB0_CHRG_DETECT_STATUS.

If I set FORCE_DETECT bit in the USB_ANALOG_USB0_CHRG_DETECT register I'm able to distinguish three different conditions from USB_ANALOG_USB0_CHRG_DETECT_STATUS register:

• nothing is connected to USB: PLUG_CONTACT = CHRG_DETECTED = DM_STATE = DP_STATE = 1 (all the 4 bits to 1)

• a dedicated charger is connected: PLUG_CONTACT = 0 CHRG_DETECTED = DM_STATE = DP_STATE = 1 (three bits to 1 and one bit to 0)

• a host device (my laptop): PLUG_CONTACT = DM_STATE = DP_STATE = 0 CHRG_DETECTED = 1(three bits to 0 and one bit to 1)

Some questions came out:

1. how does bit CHRG_DET_STATUS in USB_ANALOG_USB0_CHRG_DETECT register works? This is a read-only bit, but it's always zero (even if the charger is conneted).

2. based on reference manual, PLUG_CONTACT bit should be 0 when the USB plug has not been contacted, but in my test it's the opposite. How it is supposed to work?

[CarlosCasillas]

Hi Vix,

You could take a look at Chapter 14 “USB Device Charger Detection (USBDCD) Module” of the “Kinetis Peripheral Module Quick Reference” document, as a reference:

http://www.nxp.com/files/32bit/doc/quick_ref_guide/KQRUG.pdf

Hope this will be useful for you.

Best regards!

/Carlos

[vix]

Hi Carlos,

the content of Chapter 14 “USB Device Charger Detection (USBDCD) Module” of the “Kinetis Peripheral Module Quick Reference” is not so useful, because it refers to a different platform and the registers and bit definition is quite different.

The first paragraphs of chapter 14 clarify a little bit the USB charger specification, but they're almost clear.

My problem is what I see in VF61 registers when different USB chargers are connected; this seems a little bit different from what written in VFxx reference manual.