Another way of going about it, the way I choose to with
my Yamaha DD-65, is to make a software instrument with samples from the device. To do this you would need to sample each drum sound from your TD-20 into an individual .WAV file for each sample, making sure the sample begins at the VERY beginning of the .WAV file. Once you have all your drum samples organized, use the EXS24 sampler and follow the steps on this website to create a custom software instrument:
How to Create a Custom Instrument with Logic’s EXS Sampler
For step 4 you can click "Load multiple samples" rather than "New zone." This will speed up the process.
Skip step 7 and instead uncheck the "Pitch" checkbox in every sample's options. Also, check the 1Shot box for every sample.
The last step before you continue on to step 8 is to put all of your hi-hat samples into their own group and make the group polyphony "1". This will prevent the open hi-hat sound from playing when the hi-hat is closed.
Skip step 9, follow step 10, and you should be good to go!
Sorry if this post is a little rough. I have to do something in a few minutes and I just wanted to put this out here really quickly. If you have any questions, feel free to post. I've gone through this many times and this is the best solution I've found. Good luck!