Fun with resistors (home/car dock mode + more)

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Senior Member
Mar 30, 2006
Looks like the resistor(s) are actually inside the AnyWay box, instead of the usb-c plug.
As you can see in the pinout diagram, line CC is connected to the DB25 header which in turn connected to the box.
So, if anyone has the AnyWay box, the usb-c test cable, and an ohm meter they can simply measure the resistance between ground and pin 23 of the DB25 header. This way we could replicate a test cable without the expensive test jig.

I have played around with the "standard" test resistor values (300k, 523k, 619k etc) between line CC and Gnd, but wasn't able to get any results, not even download mode using a 300k resistor which works on all micro-usb phones. Either usb-c is using different values or there's something else we're missing here.
However, an interesting observation I've made, is that when flashed with combination firmware, the phone accepts most of these low level uart/modem test commands through the usb-c modem port (not the usb-serial port!) via a standard terminal (sometimes they need to be sent a couple of time for it to take, and also dialed *#0*# for test mode):

AT+GMM (Model number)
AT+HWINDICK (CPID S7 and newer)
AT+FACTORST (Warning: Forces a factory reset!)
AT+FUS? (DL mode)
AT+SIZECHECK (Storage info)
AT+SIZECHECK=1,0 (Storage info)
AT+SVCIFPGM=1,1 (Short Info)

Read commands:
AT+<command> - read
AT+<command>? - read
AT+<command>=1,0 - read
For example:
AT+PRECONFG=1,0 - reads CSC config

Write commands:
AT+<command>=2,<info> - write
For example:
AT+PRECONFG=2,XAS - writes CSC config

Hope someone steps up to the plate, and gives us the correct resistor value between CC and GND on usb-c :)
Thanks in advance.
Last edited:


Aug 16, 2010
It seems a static topic.
Any idea anybody regarding to the resistor list for a usb-c?
I am interested for activating dock mode (car or home) on a smartphone.


Senior Member
Dec 10, 2010
Just for information, all values can be found on FSA9480 datasheet:

The FSA9480 is a USB port accessory detector and
switch. The FSA9480 is fully controlled using I2C and
enables USB data, stereo and mono audio, video,
microphone, and UART data to use a common
connector port. It is designed for compatibility with CEA-
936-A car kit adapters, USB 2.0 signaling, and USB
OTG (on-the-go). The architecture is designed to allow
audio signals to swing below ground so a common USB
and headphone jack can be used for personal media
players and portable peripheral devices. Sheets/Fairchild PDFs/FSA9480.pdf

Note: on page 13 there are some other values I don't quite understand.
Can someone have a look?


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    We've already established that a resistor on the micro USB port can be used to force the Galaxy S into download mode, but the USB switching chip used on the phone has a lot of other capabilities that are triggered by different resistors between pin 4 and 5 of the plug.

    Update 6 March 2011: Confirmed modes so far:
    Desk Dock: 365K (also works with 1K)
    Car Dock: 619K
    In these modes audio output can be switched to pins D- and D+ of the USB port (D- is left) but this is not done by default, see this thread.

    Serial port/UART: RID_FM_BOOT_OFF_UART (523K)
    Read the rest of this thread for more details on using this port.
    Other resistor values that also enable the serial port:
    RID_AUD_DEV_TY_2 (80.07K): Doesn't switch the phone on, but produces bootlog output on the serial port when you switch it on manually. The bootlog output only starts partway through the second bootloader, rather than from the start of the primary bootloader.
    UART_CABLE (150K): Same as RID_AUD_DEV_TY_2

    Download mode:
    301K (this thread).

    Here is a list of all the resistor values, from fsa9480_i2c.h in the open source code for JPM. The resistor goes from pin 4 to pin 5 of the micro USB plug (full details on how to wire this up are in this thread). When you connect the plug with the resistor (in Froyo) you should see some messages from the fsa9480 driver in the kernel log, which you can view with the "dmesg" command.

    RID_USB_OTG_MODE,	/* 0 0 0 0 0 	GND 		USB OTG Mode              */
    RID_AUD_SEND_END_BTN,	/* 0 0 0 0 1 	2K		Audio Send_End Button*/
    RID_AUD_REMOTE_S1_BTN,	/* 0 0 0 1 0 	2.604K		Audio Remote S1 Button */
    RID_AUD_REMOTE_S2_BTN,	/* 0 0 0 1 1 	3.208K		Audio Remote S2 Button                         */
    RID_AUD_REMOTE_S3_BTN,	/* 0 0 1 0 0 	4.014K		Audio Remote S3 Button */
    RID_AUD_REMOTE_S4_BTN,	/* 0 0 1 0 1 	4.82K		Audio Remote S4 Button */
    RID_AUD_REMOTE_S5_BTN,	/* 0 0 1 1 0 	6.03K		Audio Remote S5 Button */
    RID_AUD_REMOTE_S6_BTN,	/* 0 0 1 1 1 	8.03K		Audio Remote S6 Button */
    RID_AUD_REMOTE_S7_BTN,	/* 0 1 0 0 0 	10.03K		Audio Remote S7 Button */
    RID_AUD_REMOTE_S8_BTN,	/* 0 1 0 0 1 	12.03K		Audio Remote S8 Button */
    RID_AUD_REMOTE_S9_BTN,	/* 0 1 0 1 0 	14.46K		Audio Remote S9 Button */
    RID_AUD_REMOTE_S10_BTN,	/* 0 1 0 1 1 	17.26K		Audio Remote S10 Button */
    RID_AUD_REMOTE_S11_BTN,	/* 0 1 1 0 0 	20.5K		Audio Remote S11 Button */
    RID_AUD_REMOTE_S12_BTN,	/* 0 1 1 0 1 	24.07K		Audio Remote S12 Button */
    RID_RESERVED_1,		/* 0 1 1 1 0 	28.7K		Reserved Accessory #1 */
    RID_RESERVED_2,		/* 0 1 1 1 1 	34K 		Reserved Accessory #2 */
    RID_RESERVED_3,		/* 1 0 0 0 0 	40.2K		Reserved Accessory #3 */
    RID_RESERVED_4,		/* 1 0 0 0 1 	49.9K		Reserved Accessory #4 */
    RID_RESERVED_5,		/* 1 0 0 1 0 	64.9K		Reserved Accessory #5 */
    RID_AUD_DEV_TY_2,	/* 1 0 0 1 1 	80.07K		Audio Device Type 2 */
    RID_PHONE_PWD_DEV,	/* 1 0 1 0 0 	102K		Phone Powered Device */
    RID_TTY_CONVERTER,	/* 1 0 1 0 1 	121K		TTY Converter */
    RID_UART_CABLE,		/* 1 0 1 1 0 	150K		UART Cable */
    RID_CEA936A_TY_1,	/* 1 0 1 1 1 	200K		CEA936A Type-1 Charger(1) */
    RID_FM_BOOT_OFF_USB,	/* 1 1 0 0 0 	255K		Factory Mode Boot OFF-USB */
    RID_FM_BOOT_ON_USB,	/* 1 1 0 0 1 	301K		Factory Mode Boot ON-USB */
    RID_AUD_VDO_CABLE,	/* 1 1 0 1 0 	365K		Audio/Video Cable */
    RID_CEA936A_TY_2,	/* 1 1 0 1 1 	442K		CEA936A Type-2 Charger(1) */
    RID_FM_BOOT_OFF_UART,	/* 1 1 1 0 0 	523K		Factory Mode Boot OFF-UART */
    RID_FM_BOOT_ON_UART,	/* 1 1 1 0 1 	619K		Factory Mode Boot ON-UART */
    RID_AUD_DEV_TY_1_REMOTE,	/* 1 1 1 1 0 	1000.07K	Audio Device Type 1 with Remote(1) */
    RID_AUD_DEV_TY_1_SEND = RID_AUD_DEV_TY_1_REMOTE ,		/* 1 1 1 1 0 	1002K		Audio Device Type 1 / Only Send-End(2) */
    RID_USB_MODE,		/* 1 1 1 1 1 	Open		USB Mode, Dedicated Charger or Accessory Detach */
    Thanks, I had a quick look and they no longer use the FSA9480 chip for the USB interface, instead it looks like they use the MAX77693 chip, same as the Galaxy SIII. There is a resistor table for cable detection in the code that has the same values for the car dock etc.:
    	ADC_DOCK_VOL_DN		= 0x0a, /* 0x01010 14.46K ohm */
    	ADC_DOCK_VOL_UP		= 0x0b, /* 0x01011 17.26K ohm */
    	ADC_SMARTDOCK		= 0x10, /* 0x10000 40.2K ohm */
    	ADC_AUDIODOCK		= 0x12, /* 0x10010 64.9K ohm */
    	ADC_CEA936ATYPE1_CHG	= 0x17,	/* 0x10111 200K ohm */
    	ADC_JIG_USB_OFF		= 0x18, /* 0x11000 255K ohm */
    	ADC_JIG_USB_ON		= 0x19, /* 0x11001 301K ohm */
    	ADC_DESKDOCK		= 0x1a, /* 0x11010 365K ohm */
    	ADC_CEA936ATYPE2_CHG	= 0x1b, /* 0x11011 442K ohm */
    	ADC_JIG_UART_OFF	= 0x1c, /* 0x11100 523K ohm */
    	ADC_JIG_UART_ON		= 0x1d, /* 0x11101 619K ohm */
    	ADC_CARDOCK		= 0x1d, /* 0x11101 619K ohm */
    #if defined(CONFIG_MUIC_DET_JACK)
    	ADC_EARJACK		= 0x1e, /* 0x11110 1000 or 1002 ohm */

    But there are a lot of conditional compile settings e.g.
    #if !defined(CONFIG_MUIC_MAX77693_SUPPORT_CAR_DOCK)

    So they may have compiled it without this activated for the Note 2. Possibly the SGS III forums have more info?
    I got PM'ed by a user for a feature request on the Note 2, currently by default it is compiled with:


    Car dock entry is missing in the default defconfig. The S3 has none of these options checked:

    # CONFIG_MUIC_MAX77693_SUPPORT_CAR_DOCK is not set

    Also, keep in mind we're talking international S3, US version has different PMICs.

    So here's a kernel for both devices with all the three options enabled: S3 build upon this kernel, and the N2 on this one (Almost the same).

    Again, both these have:


    I currently have no device/dock to test this functionality other than simple OTG, so I post it here for because of the specificity of the request. If it works I will keep it for both in the stable kernels.

    Edit: I have moved this functionality onto the my main kernels and you should visit the threads linked above for downloads of new versions.
    Some notes about the UART:

    The UART device is /dev/ttySAC2 but you need to create a device node for it as described in this file from the kernel source:

    So use this command (root required):
    mknod ttySAC2 c 204 66

    The UART is switched between the MODEM (radio) and PDA (CPU) by the device /sys/devices/virtual/sec/switch/uart_sel

    You can see what the current state is with this command:
    cat /sys/class/sec/switch/uart_sel
        [UART Switch] Current UART owner = PDA

    You can change the state with:
       echo PDA> /sys/class/sec/switch/uart_sel
       echo MODEM> /sys/class/sec/switch/uart_sel

    You can tell when it's connected to MODEM because it will respond to AT commands, e.g.
     Manufacturer: SAMSUNG
     Model: I9000
     Revision: I9000XXJPP
     IMEI: ***************

    The baud rate is set to 115200 at boot time, I don't know how to change it as yet.
    Hi! After modding USB port to behave as UART, is it possible to use this port for custom data and not just for debug output? For instance, I would like to open ttySAC2 port with putty and enter some text which would then be transferred to my PC.
    Yes the ttySAC2 port works fine. In some configurations the serial port that's connected to the USB pins gets switched to the MODEM after boot and you need to switch it back, like this (from a terminal command line on the phone):

    echo PDA > /sys/class/sec/switch/uart_sel
    echo hi>/dev/ttySAC2 (you should see "hi" on a connected serial terminal).
    Noob question but on the list of resistor values does the */11101 indicate the usb pins to connect? or is it always 4 and 5?
    It is always pins 4 & 5. The binary bits indicate the value in the ADC (Analog to Digital Converter) register on the chip, under "//CR7 : ADC Register" in the fsa9480_i2c.h file.