The TI SR-16 calculator uses a TMS1000 with instruction TDO augmented to decrement Y.

SR16 keypad layout
------------------------------
    K1      K2      K4      K8
R0  ~       -       rcl     0
R1  ~       +       CE      1
R2  ~       x       +/-     2
R3  ~       /       .       3
R4  ~       =       ee      4
R5  ~       sum     sto     5
R6  ~       1/x     yx      6
R7  ~       x2      ~       7
R8  ~       10x     ex      8
R9  ~       sqrtx   ~       9
R10 C       log     lnx     ~