Yes! The 6800 Trainer was only MPU Learning System in the academic institutions and the universities. I started with ETW-6802 (Fig-1) which had no Serial Communication Link and even no Assembler. We did manual coding and entered the program codes using Hex Keypad. After entry, we enetered the beginning address of the program and then hit the GO key and the program got executed. Result appeared on 6-digit display unit.
Figure-2: HeatKit 6802 MPU Trainer
What was happening there when the GO key was hit - there was no answer in the User/Technical Manual. Then I started studying the 6802 data sheets to design/build my own 6802 based Trainer (Fig-2). And the rest was the history of designing /building/selling 8085/8086/80286/89S52 Trainers with Full Serial Link and Text/GUI Interface.
Figure-2: 6802 Based Wire-wrapped Trainer
Have a nice time!