Blaupunkt Reno reset code
 

I have a 1990 Porsche 944 since new, with a Blaupunkt Reno unit. The battery is disconnected over the winter. I HAVE the radio code and manual. I screwed up the code entry three times or more and now the display shows "----" instead of "CODE". It thinks it has been stolen, I guess. How do I get it back to the CODE display to let me enter the activation code? I have let it sit for 2 months without battery power. A button to push, perhaps?