Goodness Gracious...

Just go with one of the simple two byte transfer schemes suggested. Out of your 37 commands defined I find it really really really hard to believe that two bytes sent is any sort of huge complication at all.

Transfer size??? Hurrumph - If you are hand typing these from a terminal emulator there could hardly be a timing constraint that needs to have the transfer duration be squeezed down really tight. If it was such then just double the baud rate!! It is also hard to believe that every one of 37 commands is a parameter free and/or response free entity. Any additional bytes sent / received as what I suspect averages 3 to 5 bytes per command means that adding one more byte to the mix is low overhead!!!

Keep in mind that using a two byte sequence that uses a relational coding ( as I described here http://www.8052.com/forumchat/read/183290 ) is way way better error detection coverage than trying to jam a coded error detection into one byte.

In implementation since the universe of cases is small there is not even a need to "error check" on the receiving end. Just compare commands on the basis of 37 16-bit values.

In my way of thinking the choice is obvious and need not require a lot more pondering.

Michael Karas