I would like to connect this GPS sensor: https://buy.garmin.com/shop/shop.do?pID=161 to an mbed serial port. The GPS port can be connected to a PC RS232 port even if the level is 0-3V. The manual said "compatible with RS232 or TTL voltage levels, RS-232 polarity" Because the voltage swing is limited to 3V, you can connect it to a RS232 PC port and also directly to an MCU serial port but with inverted level. I've connected it to an FTDI FT232 USB to serial, using a MAX232 chip to invert the RX & TX levels.

I know that Microchip PIC UART modules can be configured in normal or inverted level mode. I'm not able to find this kind of configuration in mbed serial library. Does anyone know if this is possible too on mbed with a special configuration, but without using additional hardware.

thanks in advance.

Not a direct answer to your query but it may help.

For my microcontroller projects I routinely use a 74HC14 (or variant) as a serial interface chip. It is a hex inverter with schmidt trigger. It provides the inversion needed and the schmidt trigger cleans up the incoming serial data. I put a 10K ohm resistor in line with the serial input (and another one to ground) to limit the current from signals out of the power supply range. It works quite well and is simpler and cheaper than MAX232s and such.

I often use two 74LVC1G14s, a signal inverter SMT version of the 74HC14.

Thank you for your replay. So it looks alike there is no software way to do that.