I have designed the PCB:
And I have written a short demo program (actually all programs are short for the TD4):
The demo shows the basic OpCode syntax and how data is written to or read from memory. The "... + 0" etc. for all the OpCodes, is the immediate data that is always added to the source data before being written to the destination register. The OpCode structure is much more pleasant to use than TTA. An expanded version (i.e. increased address space) would need to be able to access an ALU (perhaps in the memory address space) to be considered a complete CPU. It remains to be seen how efficient this set of OpCodes would be in an expanded CPU.
Here are the current OpCodes: