what is difference between XT09-MI and XT09-MI-revD

i have purchased module i recd some module of XT09-MI and some are XT09-MI-revD.

XT09-MI-revD module works but other is not working. pl. help


Rev D just means that it is the revision D version of that module. Same module, same code and both should talk to each other. The only difference is just a few different components under the shield.