RS232 Signal Level

RS232 (EIA-232, TIA-232-F) standard allows signal level +-3 .. 15V operating signal level voltage on the line.

Also: [Indefinite short circuit to ground or to any voltage level up to ±25 volts].

For 3.3V systems (BT-RS232 adapters and some STM32 devices), ST3232/MAX3232 chip is used as line drivers.

3 types of linedrivers were previously used in BT-RS232 and STM32:

All pass tests reproducibly with FTDI USB-RS232 adapters, and VEMS ECU with texas MAX232 (or MAX232I).

USB is known for occasional compatibility problems (mostly windows drivers, but sometimes more tricky, involving supply current rating, with USB hubs or not), compatibility issues with 3 line-RS232 devices (where DTR, RTS, ... signals are not used, only RX,TX and GND) have been almost nonexistent and unheard of... (except forgotten ground or miswiring)


See also