UART¶

There is an in-depth article covering several Samsung devices in the SamsungSerial page

Settings¶

Device and documentation	I/O voltage	ID<->GND	SOC TX	SOC RX	switch	stock bootloader settings	Comments
GT-I9100		510k9	D-	D+	MAX8997	UART settings: ttySAC2 115200 8N1 To get the UART enabled at boot with the stock bootloader: * Power the phone off and remove the battery * Put a battery in * Hold the select button * Plug the UART * Release the select button	At some point the boot procedure switches to the modem UART, it's probably some linux driver doing that
GT-N7000	510k9	D-	D+		UART settings: ttySAC2 115200 8N1
GT-I9100G_CHN_CHN	1.8V8 ?	619k9	D-	D+	?	UART settings: 115200 8N1	Very few prints from Xloader, the next bootloader used by Android 2.6.3 doesn't seem to print much
GT-I9300	1.8V1	619 kOhms3	D-	D+	MAX776935	UART settings: 115200 To increase verbosity during boot: * Power off the phone and remove the battery * Put a battery in * Press the hold the volume-down button * Plug the UART and wait for the first lines to be printed * Release the volume-down button	It gives a shell once Replicant 6 has booted
GT-I9305
GT-N7100	?
GT-N7105	?
Galaxy Nexus (GT-I9250)		619 kOhms4	D+	D-	FSA94807	UART settings: * By default: ttyFIQ0, 115200 8N1 * After patching Linux: ttyO2, 115200 8N1 See GalaxyNexusI9250SerialConsole for more details.
Nexus S		150 kOhm			FSA9480
Optimus Black (P970)	1.8V6	N/A2			DP3T
ODROID-U3, console UART	1.8V	connector				UART settings: ttySAC1, 115200 8N1
ODROID-U3, IO pins UART	1.8V	connector				UART settings: ttySAC0, 115200 8N1

¹ Measured between USB GND and USB VCC

² Code is required to use the switch as you need to configure both the MUIC and DP3T switch

³ See The related driver source code

⁴ See the postmarketOS wiki page on Serial debugging

⁵ See the driver and the ifixit teardown

⁶ Reference: OptimusBlackSerial

⁷ See board-tuna-connector.c fsa9480.c in kernel_samsung_tuna

⁸ Works, as it was tested on the device. TODO: measure the voltage, as lower UART voltages often works with higher voltage levels.

⁹ Works, as it was tested on the device. TODO: look the official reference in the driver for it.

Datasheets¶

• FSA9480.pdf

Interesting links¶

• There is a page on Serial debugging on the postmarketOS wiki that contains information for using the serial port for many smartphones models.
• mv-uart A serial port adapter with configurable voltages (and GPIOs)
• DHylands_SGS2_SerialAdapter : A very compact setup but with fixed resistor value.