I want encodes the word 0xe5910004 in the corrispective instruction. From the suggestions of the exercise, the instruction should be of the block data transfers type. The theoretical construct should be:enter image description here
My problem is that I don’t know how I should convert the lowercase letters to binary. For example, if I had the uppercase letter E instead of the lowercase e I would know that it corresponds to the value 1110. If I convert the lowercase letter e to binary I would have something like 01100101 (if correct).

I suppose I should switch from 8-bit to 4-bit but I don’t know how. In this way I wouldn’t know how to fill the bits correctly in the respective cells to encode the instruction it represents.
I hope someone will give me a clear explanation in the steps.
Thank you