Definitely not standard RS232 or even standard serial really. It's a single wire open collector type data line. Also it's technically not even 1500 baud really. It sends 0s and 1s by different length on and off pulses. It just so happens that you can 'shonk' the same effect by talking at roughly 1500 baud and sending some special characters. For each 4 bits of data I actually send two bytes (ie 16 bits) of 1500 baud 8N1 data.