What Is ISP Pinout

ISP (In-System Programming) is a direct hardware access method used by mobile repair technicians to communicate with a device's NAND flash storage — bypassing the main CPU boot sequence entirely. Rather than relying on the device's operating system or bootloader to be functional, ISP establishes a connection directly to the UFS or eMMC pads on the PCB. This allows read, write, and erase operations even when the phone is completely dead or its software is corrupted. For the Samsung SM-A905 (Galaxy A90), ISP access is particularly valuable because standard software routes such as EDL (Emergency Download Mode) may be secured or inaccessible on carrier-locked units.

SM-A905 ISP Testpoint Map

The Samsung SM-A905 uses a UFS 2.1 flash storage interface rather than a traditional eMMC bus. The ISP testpoints are located on the rear side of the main PCB, near the UFS chip. Technicians must remove the motherboard from the chassis and identify the relevant pads under magnification. The core ISP signals for UFS-based ISP boxes are as follows:

  • CLK — UFS reference clock pad
  • DATA0 (Rx/Tx lanes) — Differential data lane pads (Rx+, Rx−, Tx+, Tx−)
  • VCC — Primary storage supply voltage (2.7–3.6 V)
  • VCCQ — I/O supply voltage (1.8 V)
  • GND — Common ground reference pad
  • RST — Reset signal pad

Note: Exact pad coordinates and silk-screen labels for the A905 PCB are not universally published. Always cross-reference with a verified board schematic or ISP adapter pinout card before making contact.

When Technicians Use ISP

ISP access on the SM-A905 is typically employed in the following scenarios:

  • Dead boot / no power: When the device fails to power on after a failed firmware flash or water damage.
  • FRP (Factory Reset Protection) lock: When the Google account lock cannot be bypassed through software methods.
  • Pattern or PIN lock: When the lockscreen cannot be cleared via recovery or ADB.
  • Failed EDL mode: When the device does not enter Emergency Download Mode or EDL is rejected by Qualcomm programmers.
  • Firmware backup: Creating a full sector-level image of the UFS storage before further repair attempts.

How to Perform ISP Access

Follow these steps carefully to establish ISP connection on the SM-A905:

  • Power off the device completely and disconnect the battery.
  • Disassemble the phone and remove the main PCB.
  • Clean the ISP testpoint area with isopropyl alcohol (99%).
  • Identify UFS ISP pads using a verified schematic or ISP adapter card.
  • Solder thin wire leads or use a dedicated ISP pogo-pin adapter to the pads.
  • Connect leads to your ISP tool (e.g., EasyJTAG Plus, UMT, or Medusa Pro II) according to the tool's UFS pinout card.
  • Launch the ISP software, select Samsung SM-A905, and initiate the desired operation (read, erase, or write).
  • After completion, desolder wires, reassemble the device, and test.

Safety Tips and Precautions

Working at the ISP level carries significant risk. Observe these precautions:

  • Always disconnect the battery before soldering to ISP pads — incorrect voltage can instantly destroy the UFS chip.
  • VCCQ must be 1.8 V. Applying 3.3 V to I/O lines will permanently damage the UFS controller.
  • Use a high-quality soldering iron with a fine tip; excessive heat will lift pads and render the board irreparable.
  • Take a full UFS sector backup before any erase or write operation.
  • Verify your ISP tool's UFS compatibility — not all boxes support the M.2-style UFS interface used in the A90.
  • Work in an ESD-safe environment with a grounded wrist strap.

Pin / Test Point Reference

PinDescription
CLKUFS reference clock signal pad on PCB — Exact pad location requires verified schematic
TX+UFS differential transmit positive lane — Part of high-speed serial interface
TX-UFS differential transmit negative lane — Part of high-speed serial interface
RX+UFS differential receive positive lane — Part of high-speed serial interface
RX-UFS differential receive negative lane — Part of high-speed serial interface
VCCPrimary UFS storage power supply (2.7–3.6 V)
VCCQUFS I/O supply voltage — must be 1.8 V — Applying incorrect voltage destroys UFS
GNDGround reference pad
RSTUFS reset signal pad — Exact pad location not publicly confirmed

Tools required: EasyJTAG Plus with UFS adapter, UMT (Ultimate Multi Tool), Medusa Pro II, Riff Box 2 (with UFS support), ISP pogo-pin adapter for Samsung UFS boards, Fine-tip soldering iron, 99% isopropyl alcohol, ESD wrist strap

Supported operations: Read Firmware / UFS Sector Backup, FRP Erase, Dead Boot Repair, Pattern / PIN Lock Removal, Firmware Write / Restore, IMEI Repair (where legally permitted)

⚠ Safety note: VCCQ must not exceed 1.8 V. Disconnect battery before all ISP work. Incorrect voltage will permanently destroy the UFS chip. Always back up before erasing.