Currently working on a RS232 add-on card for the Z80-MBC2.

As the uTerm board, it has a power supply for the Z80-MBC2 and a "transparent" USB-TTL adapter connector, so you can upload firmware or load an Intel-Hex file (with iLoad) while the card is inserted. Both the "mixed" power supply scenarios (USB-TTL adapter not powered from USB but Z80-MBC2 powered and vice-versa) are managed.

Here connected to an Ampex 210 terminal (sold and relabeled by Kyber):