I was wondering what logic levels the serial port of the Jornada 720 and 820. I've been considering making myself a cable to connect it to my Arduino which runs off 5V, but I'm not sure if I need to do a level conversion.
Somewhere in the back of my head I thought I read somewhere that RS232 is compatible with 0V/5V levels (as opposed to the regular 12V levels a pc uses), but I'm not really sure what the Jornada really delivers. Can anyone point me in the right direction here?
Almost all serial ports use +12V/-12V as their low/high signal bit. Just because a device is powered off a lower voltage doesn't mean the serial port uses a lower voltage signal...and most don't. Voltage levels from the 5V state are usually increased to 12V by charge pumps (capacitors) to get to the proper operating state.
Back in the J720 day, P2s were the common desktops, and P3s were just coming into the market. They all used the standard RS232 voltages.
I know you might read about 5V serial ports, but that's usually misleading as they are probably talking about TTL serial signals...which are always internal to the motherboard where 5V is the standard.
Most serial ports are compatible with lower voltages as low as 3V. Certainly not 0V since there really is no 0V state on the port as the voltage signals are either positive or negative. The advantage of the higher 12V is obvious...longer cable runs with more signal stability....
Okay, thanks! I remembered, even if it was +5V, it would still be -5V in that case so hooking it up directly would be a terrible idea either way. I'll just put a MAX232 between and all should be good
