What Is ISP Pinout

ISP (In-System Programming) is a direct hardware flashing method that allows technicians to communicate with the eMMC storage chip on the Samsung SM-ACE 4 (G313) PCB without using the standard USB boot route. By connecting a compatible programmer directly to the eMMC test pads on the motherboard, it becomes possible to read, write, or erase firmware data at the chip level. This technique bypasses the device's main CPU boot sequence entirely, making it invaluable when software-based flashing methods are unavailable or have failed. For the G313, ISP access gives technicians full control over the flash storage, enabling firmware restoration, partition repair, and security data removal.

When to Use ISP

ISP should be considered when conventional flashing tools and USB methods are no longer viable. Common scenarios include:

  • Dead boot / hard brick: The device powers on but shows no display, gets stuck on logo, or does not respond to any boot mode.
  • Failed OTA or manual flash: A corrupted or interrupted firmware update has left the device unresponsive.
  • FRP (Factory Reset Protection) lock: The device is locked to a Google account and software FRP bypass methods have not succeeded.
  • Pattern or PIN lock: The screen lock cannot be removed through recovery or ADB.
  • eMMC partition errors: Filesystem corruption requiring direct partition-level repair or rewrite.

G313 ISP Test Points

The Samsung SM-ACE 4 G313 uses a Spreadtrum-based platform. The eMMC ISP test points are located on the rear side of the motherboard. Technicians must remove the PCB from the chassis and identify the labeled pads near the eMMC package. The standard eMMC ISP interface uses eight signals. Exact pad coordinates on the G313 PCB have not been independently verified in authoritative documentation; technicians should cross-reference with a confirmed PCB diagram or multimeter continuity testing before connecting any programmer.

Flashing Procedure Overview

To perform ISP flashing on the G313, follow this general procedure:

  • Fully disassemble the device and remove the motherboard.
  • Clean the ISP test point area with isopropyl alcohol.
  • Solder or use pogo-pin jigs to connect the ISP programmer to the CLK, CMD, DAT0, VCC, VCCQ, and GND pads.
  • Connect the programmer to a PC and launch the appropriate software (e.g., EasyJTAG Plus or UMT).
  • Power the board via the programmer's VCC supply — do not connect the battery simultaneously unless the tool requires it.
  • Detect the eMMC chip, select the correct firmware or operation, and execute the read/write/erase command.
  • After completion, disconnect safely, reassemble, and test the device.

Safety Tips and Warnings

Working at the ISP level carries significant risk of permanent damage if proper precautions are not followed:

  • ESD protection: Always use an anti-static wrist strap and work mat. Static discharge can permanently destroy the eMMC or CPU.
  • Voltage regulation: The G313 eMMC operates at 3.3 V (VCC) and 1.8 V (VCCQ). Applying incorrect voltages will destroy the chip instantly.
  • Backup first: Always perform a full eMMC read/backup before writing or erasing any data.
  • Solder carefully: Excessive heat on test pads can lift traces or damage the PCB substrate. Use a fine-tip iron at controlled temperature.
  • Use verified firmware: Only flash firmware confirmed for the G313 model to avoid bootloader mismatches.

Pin / Test Point Reference

PinDescription
CLKeMMC clock signal test pad — Exact PCB location unverified — confirm with continuity test
CMDeMMC command signal test pad — Exact PCB location unverified
DAT0eMMC data line 0 test pad — Exact PCB location unverified
VCCeMMC main power supply — typically 3.3 V — Verify voltage before connecting
VCCQeMMC I/O power supply — typically 1.8 V — Verify voltage before connecting
GNDGround reference test pad — Multiple ground points available on PCB
RSTeMMC reset line — May not be exposed as dedicated test pad on G313
DAT1–DAT7Additional eMMC data lines (bus width) — Only DAT0 required for ISP 1-bit mode on most programmers

Tools required: EasyJTAG Plus, UMT (Ultimate Multi Tool), Medusa Pro Box, Pogo-pin ISP jig or fine solder wire, Anti-static wrist strap and mat, Regulated DC power supply, Multimeter (for continuity testing)

Supported operations: Read Firmware / eMMC Backup, Write Firmware, FRP Erase, Dead Boot Repair, Pattern / PIN Lock Remove, Partition Repair

⚠ Safety note: Incorrect voltage (VCC >3.3 V or VCCQ >1.8 V) will permanently destroy the eMMC. Always backup before writing. Use ESD protection at all times.