After having the whole system debugged with the NAC pcb, having display multiplexing working, it was time to replace the NAC by the real thing, the 1x1" CPU.

After having corrected a few bad soldered pins, it was still impossible to program the microcode. When reading the flash, all locations returned 0x00. Strange, because unprogrammed locations normally return 0xFF.....

Back to the datasheet......  

Well everything that CAN go wrong, WILL go wrong. So if you don't check the datasheet for the pinout....  The pinout for the TSOP is different from the DIP pinout !   Beginner's mistake, I assumed they would be the same without even thinking about it. 

So this means re-doing the pcb design and order new PCB's. Today, I will continue to program the 6-digit clock.