Pricom

Pricom made a very nice DCC protocol analyzer with an LCD screen.

http://www.pricom.com/Trains/DCCTester.shtml

DCCT Both

Apparently no longer sold because of lack of the LCD screen.

You can update the firmware yourself, using a special cable:

Wiring for firmware update cable.

descriptionRJ11DB9color
NC1  
ground25yellow
xmit > pc32brown
rcv < pc43red
ground55yellow
NC6  

 

current and last firmware version: v1.52

Download page for the Pricom tester

If you find one, buy it.

 

NCE also makes a packet tester, see the NCE page.

Weather Underground PWS KCACARLS78