This is one of the more interesting machines. This machine includes an accumulator, and each instruction has the single address. Calculate A - Acc, store this in both A and Acc, and skip the next instruction if the subtraction resulted in a borrow. Even simple operations like move turn out not to be since skips may not occur where we want them. This machine depends heavily on self-modifying code and about 11K of lookup tables.
Most operations turn out to be straightforward if a bit tedious.
Most arithmetic operations require splitting each byte into halves for the operation, then combining them to get the final result. One exception is jumps - since only one byte of the PC can be changed at a time. Jumps are also implemented differently. This latter write causes a jump to occur to the specified location. This machine also takes full advantage of the ALU to assist with all instructions.