Problem with reading i2c signal from slave

Hi,

I connected 5V PIC18F4520 to GLCD (GLCD-FLEXEL), through I2C lines.

The GLCD's datasheet says:
- I2C signals are 5V tolerant, provides communication with 3.3V and 5V devices
- Use one power supply + 5V, includes 3.3V voltage regulator for LCD

Does it mean that when the I2C transmit signal to the 5V PIC, the signals will be 5V?

I ask it because, I manage to write data from the PIC (Master) to the GLCD (Slave) via I2C,
BUT I don't manage to read any data from the GLCD (Salve) by the PIC (Master).

I suspect it might be that the GLCD transmits in 3.3V and therefore the PIC can't read it as it's too low (or it just reads zeros).

I don't have an 'scope yet to verify it.

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Check the online auction.