5-volt tolerant Bluetooth module is not 5-volt tolerant

[Tunelabguy]

I am trying to get a Bluetooth module to interface with my 5-volt microprocessor's serial connection. The Bluetooth module (SPBT2632C1A from ST Microsystems) operates at 2.7 volts. The TXD serial output from the Bluetooth module is supposed to be 5-volt tolerant, according to the datasheet. I have tried to pull it up to 5-volts with a 3.3k resistor, but it will not budge above 2.1 volts. This is not high enough to be detected as a logic high by my PIC micro's serial input pin. The serial connection in the other direction is working just fine with a direct connection. I could have designed in a level shifter when I was designing the circuit board, but I thought a pull-up would be sufficient. Any ideas on what "5-volt tolerant TXD" means to ST in this context?

 

[barry]

5 volt tolerant means it can TOLERATE 5volts without damage. It doesn't mean you can pullup an output to 5V.

 

[Tunelabguy]

5 volt tolerant means it can TOLERATE 5volts without damage. It doesn't mean you can pullup an output to 5V.

That interpretation makes sense for inputs to the device, but not for outputs. An output from a device is producing the voltage on the pin. It will never produce more than 3-volts if it is a 3-volt device. What else could 5-volt tolerant mean when applied to outputs other than that you can pull it up passively to 5 volts? (The datasheet specifically said both the TXD and the RXD pins are 5-volt tolerant).