I've been using this adapter for 9 years now (the same original one that I bought all that time ago) and I have never ever failed to connect to anything or had issues with communications dropping out. It's expensive but after trying many of the cheap shitters out there this is in a completely different league. Using this over the others was like night and day.

http://uk.rs-online.com/web/p/emi-fi...ories/0385180/

I used this specifically to map an Omex 600 ECU but the ECU communicated at quite a slow speed for what I had it set to. Had to slow the baud rate down a little but it worked perfectly.

You can probably buy it cheaper elsewhere as RS always have retail listed on their site.