The fx-CG20 OS updater uses
protocol 7.00 as well. Function 0x56 (upload'n'run)
loads 0x00010683 bytes at 0x880D1B00. Startaddress 0x880D1B00, too.
Luckily the bootcode OS updater works well. The same OS version can be installed repeatedly. Hence, the OS updater can be used to recover from a corrupted OS.
Trigger the bootcode OS update by simultaneously holding down F2, 4 and Ac/ON and pressing the RESTART-button (the calc should show a blank display after releasing the keys). Finally press 9 and x consecutively (hold down 9 and x about a second each).