Could you post a picture?
I once flew BAe 146s which had a sort of car radio sized navigation unit with just a knob on each end, a couple of push buttons and a one or two line green LED display. To enter a way-point, one knob selected the position of the letter you wanted to change, and the other knob turned to select a letter or a numeral. So to input 'NEDUL' for example, you would turn the first knob to move the cursor to the first letter position, then the second knob all the way through the alphabet until you got to 'N'. Then you rotated the first knob to select the second letter position, and rotated the second knob to select 'E' etc, etc. When you were done, you pressed one of the knobs to enter that way-point into your "flight plan". I say flight plan, but it could only store a few way-points, 12 maybe, and was very basic. No speeds or altitude restrictions. It just gave a steer command onto the HSI or the RMI, or something - can't remember now.
Anyway, the knobs saved on panel space - by not needing to have a dedicated key for each alphanumeric and all the functions. Is the Embraer 'knob' system similar perhaps?