树莓派4（RPi4）搭载24LC512的I2C读写异常问题咨询

Hey there, let's work through this EEPROM issue together—I've dealt with similar I2C quirks before, so here are actionable steps to fix the read/write mismatch:

• Fix the address pointer format first!
  The 24LC512 is a 512Kbit (64KB) EEPROM, which requires a 16-bit address pointer (two bytes) instead of the 8-bit one you're using. Your original i2cset command only sends the low byte of the address (0xff), leaving the high byte as 0x00 by default. This means you're not writing to the address you think you are, and the read command is also misaligned. Use these corrected commands instead:

  # Write 0x21 to address 0x00ff (full 16-bit address)
  i2cset -y 1 0x50 0x00 0xff 0x21 i
  # Wait for EEPROM write cycle to complete (critical!)
  sleep 0.01
  # Read back from the same 16-bit address
  i2cget -y 1 0x50 0x00 0xff i
  

  The trailing i tells i2cset/i2cget to use the I2C combined format for 16-bit addressing.

• Double-check hardware connections
  Even though the device is detected, flaky power or signal lines can cause partial communication failures:

  • Ensure the EEPROM's VCC is connected to the RPi's 3.3V pin (not 5V—RPi's I2C is 3.3V tolerant, and 5V can damage GPIO pins or the chip).
  • Confirm GND is solidly connected between the RPi and EEPROM.
  • Add external 4.7kΩ pull-up resistors to SDA/SCL lines if your wiring is long or in a noisy environment. The RPi has internal pull-ups, but external ones can stabilize weak signals.

• Never skip the write cycle delay
  EEPROMs don't write data instantly—24LC512 has a typical write cycle of 5ms (max 10ms). Reading immediately after writing will return stale or incorrect data as the chip is still processing the write. A 10ms sleep (sleep 0.01) is enough to ensure the write completes.

• Test with a low, safe address first
  Rule out address range issues by testing a simpler address like 0x0000:

  i2cset -y 1 0x50 0x00 0x00 0xAA i
  sleep 0.01
  i2cget -y 1 0x50 0x00 0x00 i
  

  If this works, the problem was definitely the address format in your original commands. If not, move on to adjusting the bus speed.

• Lower the I2C bus speed
  Sometimes higher bus speeds (even 400kHz, which the chip supports) can cause communication errors on the RPi, especially with longer wires. Edit /boot/config.txt and add/modify this line:

  dtparam=i2c_arm_baudrate=100000
  

  Save the file, reboot your RPi, and retry the read/write commands.

Try these steps one by one—most likely the address pointer format or write delay is the culprit. Let me know if you still hit snags!

内容的提问来源于stack exchange，提问作者Hakuna Matata