EPIA PD 5v Serial Voltage

electricitylike · 04-29-2008, 11:26 AM

I'm currently using an EPIA PD mini-ITX system for my car computer setup (it's what I had lying around for some reason). I want to hook this system up to the USART on a PIC to run the converter from my car's IEBus to the PC.

The manual for the EPIA board indicates that it supports 12v and 5v signalling levels on the serial ports (com 3 and com 4). I've got the jumpers set correctly and a serial port plugged into the com 3 pins on the motherboard, however when I check the voltages the port is still showing -12V compared to ground.

Does anyone know what these jumpers actually do? The idea I thought was that I'd be able to hook TTL level RS-232 from a PIC's USART straight to the mobo, is this not the case and I still need to use a MAX232 to convert?

_dopehead_ · 04-29-2008, 03:04 PM

well, i would think that the choice of 5 or 12V is just whether you wan't +-5v or +-12v rs232, 5v won't be ttl levels, but regular rs232 just at +-5volts, many laptops use this as well for some reason. You will probably still need a max232

electricitylike · 04-29-2008, 07:53 PM

Possible - either way it doesn't look like I'm getting any sort of change in behavior by flipping the jumpers I was just hoping someone might have an explanation as to why.