What Is ISP Pinout

ISP (In-System Programming) pinout is a direct hardware method that allows technicians to communicate with a device's NAND flash storage without relying on the phone's CPU or bootloader. Instead of sending commands through USB or software, the technician solders or physically contacts a set of test pads on the motherboard that connect directly to the UFS or eMMC storage chip. This bypasses locked bootloaders, corrupted firmware, and software-level security measures. For the Samsung Galaxy A42 5G (SM-A426), this technique is especially valuable when conventional flashing tools and download mode are inaccessible.

SM-A426 ISP Test Points

The SM-A426 uses a UFS 2.1 storage interface rather than a traditional eMMC bus, which makes ISP access more technically demanding than on older Samsung devices. The key test points corresponding to the UFS signal lines are located on the rear side of the main PCB, typically in the upper-central region near the UFS IC. The primary signals required for ISP access on this board are listed below. Note that exact pad coordinates are not publicly verified in a single authoritative source and should be confirmed with physical board inspection or a trusted board-view schematic.

  • CLK – UFS Reference Clock signal
  • DATA0 / DAT0 – Primary data line
  • CMD – Command line (UFS differential pair)
  • VCC – Core power supply to UFS (typically 2.9V)
  • VCCQ – I/O power rail for UFS (typically 1.8V)
  • GND – Common ground reference

Because UFS uses a differential serial interface (MIPI M-PHY), standard eMMC ISP adapters are not compatible. Dedicated UFS ISP adapters or probe jigs are required.

When Technicians Use ISP

ISP is the method of last resort when all software-based approaches have failed. Common scenarios for the SM-A426 include: a device stuck in a bootloop after a failed OTA or manual flash, a phone that enters EDL or download mode but is rejected by PC tools due to authentication errors, FRP (Factory Reset Protection) lock that cannot be cleared through ADB or recovery, and hardware-level dead boot where the device shows no signs of life after a bad write. ISP bypasses all of these barriers by directly interfacing with the storage chip.

ISP Access Procedure

Follow these steps carefully when performing ISP on the SM-A426:

  • Fully disassemble the device and remove the motherboard from the chassis.
  • Identify the UFS test pads using a board-view file or verified schematic.
  • Connect your ISP adapter or probe pins to CLK, DAT0, CMD, VCC, VCCQ, and GND.
  • Apply correct voltages: 2.9V on VCC and 1.8V on VCCQ before powering on.
  • Launch your ISP-capable tool (e.g., EasyJTAG Plus or UFI Box) and select the correct UFS pinout profile.
  • Perform a full backup read before attempting any write or erase operation.
  • Execute the desired operation: firmware flash, FRP sector erase, or partition repair.
  • Disconnect, reassemble, and test the device.

Safety Tips and Precautions

Working at the hardware level carries significant risk. Always observe the following precautions:

  • Use an ESD mat and wrist strap at all times — UFS chips are highly sensitive to static discharge.
  • Never exceed 1.8V on VCCQ lines; overvoltage will permanently damage the UFS controller.
  • Always perform a full chip backup before writing or erasing any sector.
  • Verify test pad connections with a multimeter before applying power.
  • Do not attempt ISP on a device under warranty unless the owner has given explicit written consent.
  • Use a regulated bench power supply — do not rely solely on battery power during ISP operations.

Pin / Test Point Reference

PinDescription
CLKUFS reference clock signal pad — Exact pad location requires board-view verification
DAT0Primary UFS data line (differential) — UFS uses differential pairs; standard eMMC adapters incompatible
CMDUFS command/control line — Part of MIPI M-PHY differential interface
VCCCore power supply for UFS chip — Typically 2.9V; verify before connecting
VCCQI/O voltage rail for UFS chip — Typically 1.8V; do not exceed
GNDGround reference for all ISP signals — Multiple ground pads available near UFS IC

Tools required: EasyJTAG Plus with UFS adapter, UFI Box, Medusa Pro II (UFS support), Regulated bench power supply, UFS ISP probe jig or fine-tip soldering station, Board-view / schematic software, ESD mat and wrist strap

Supported operations: Full UFS Chip Read/Backup, Firmware Flash (dead boot repair), FRP Erase, Partition Repair, IMEI Repair (where legally permitted), User Data Wipe

⚠ Safety note: Max VCCQ is 1.8V; exceeding this destroys the UFS controller. Always back up before writing. Use ESD protection at all times. Confirm pad locations with a board-view schematic before soldering.