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        Description of the ternary computer TRIADOR
 ══════════════════════════════════════════════════════════
  General purpose
     registers
 trits 2 1 0  (a trit can take -1,0,+1 values)
      ┌─┬─┬─┐
    R1│ │ │ │ \
      ├─┼─┼─┤ |                              Program memory
    R2│ │ │ │ |                            trits 4 3 2 1 0
      ├─┼─┼─┤ |-- main set                      ┌─┬─┬─┬─┬─┐
    R3│ │ │ │ |   of registers           a  -364│ │ │ │ │ │
      ├─┼─┼─┤ |                          d      ├─┼─┼─┼─┼─┤
    R4│ │ │ │ /                          d  -363│ │ │ │ │ │
      ├─┼─┼─┤                            r      ├─┼─┼─┼─┼─┤
    R5│ │ │ │ \                          e  -362│ │ │ │ │ │
      ├─┼─┼─┤ |                          s      ├─┼─┼─┼─┼─┤
    R6│ │ │ │ |                          s      : : : : : :
      ├─┼─┼─┤ |                                 ├─┼─┼─┼─┼─┤
    R7│ │ │ │ |                              -1 │ │ │ │ │ │
      ├─┼─┼─┤ |                                 ├─┼─┼─┼─┼─┤
    R8│ │ │ │ |                               0 │ │ │ │ │ │
      ├─┼─┼─┤ |-- extra registers               ├─┼─┼─┼─┼─┤
    R9│ │ │ │ |                              +1 │ │ │ │ │ │
      ├─┼─┼─┤ |                                 ├─┼─┼─┼─┼─┤
   R10│ │ │ │ |                                 : : : : : :
      ├─┼─┼─┤ |                                 ├─┼─┼─┼─┼─┤
   R11│ │ │ │ |                             +363│ │ │ │ │ │
      ├─┼─┼─┤ |                                 ├─┼─┼─┼─┼─┤
   R12│ │ │ │ /                             +364│ │ │ │ │ │
      ├─┼─┼─┤                                   └─┴─┴─┴─┴─┘
   R13│ │ │ │ Special register,
      └─┴─┴─┘ specifies memory segment for JP ttt
      ┌─┬─┬─┬─┬─┬─┐
   PC │ │ │ │ │ │ │ program counter register (-364..+364)
      └─┴─┴─┴─┴─┴─┘
      ┌─┐
    C │ │ borrow/carry flag (+1 borrow, -1 carry)
      └─┘

  Every 3-trit register can take values from -13 to +13:

  t2*9 + t1*3 + t0

  where t0,t1,t2 - trits (-1,0,+1)

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                 TRIADOR instruction set
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  (for lisibility we use N,O,P instead of -1,0,+1)
  ┌───────┬────────┬───────────────────────────────────────┐
  │op code│mnemonic│ description                           │
  ├───────┼────────┼───────────────────────────────────────┤
  │ NNttt │ EX ttt │ extension commands (work in progress) │
  ├───────┼────────┼───────────────────────────────────────┤
  │ NOttt │ JP ttt │ unconditional jump to R13*27+ttt      │
  ├───────┼────────┼───────────────────────────────────────┤
  │ NPttt │ SK ttt │ conditional skips of the next command │
  ├───────┼────────┼───────────────────────────────────────┤
  │ ONttt │ OP ttt │ tritwise unary operation over R1      │
  ├───────┼────────┼───────────────────────────────────────┤
  │ OOttt │ RR ttt │ copying between registers             │
  ├───────┼────────┼───────────────────────────────────────┤
  │ OPttt │ R1 ttt │ write ttt to the register R1          │
  ├───────┼────────┼───────────────────────────────────────┤
  │ PNttt │ R2 ttt │ write ttt to the register R2          │
  ├───────┼────────┼───────────────────────────────────────┤
  │ POttt │ R3 ttt │ write ttt to the register R3          │
  ├───────┼────────┼───────────────────────────────────────┤
  │ PPttt │ R4 ttt │ write ttt to the register R4          │
  └───────┴────────┴───────────────────────────────────────┘

  Additional comments:
  - ttt means a 3-trit number with values
    from NNN (-13) to PPP (+13)

  - RR ttt instruction copies a register to/from R1 or performs
    an increment/decrement over R1
    OONNN — copy R1 to R13
    OONNO — copy R1 to R12
    OONNP — copy R1 to R11
    OONON — copy R1 to R10
    OONOO — copy R1 to R9
    OONOP — copy R1 to R8
    OOPON — copy R1 to R7
    OOPOO — copy R1 to R6
    OOPOP — copy R1 to R5
    OOONN — copy R1 to R4
    OOONO — copy R1 to R3
    OOONP — copy R1 to R2
    OOOON — decrement R1, set borrow/carry flag
    OOOOO — no operation
    OOOOP — increment R1, set borrow/carry flag
    OOOPN — copy R2  to R1
    OOOPO — copy R3  to R1
    OOOPP — copy R4  to R1
    OOPNN — copy R5  to R1
    OOPNO — copy R6  to R1
    OOPNP — copy R7  to R1
    OOPON — copy R8  to R1
    OOPOO — copy R9  to R1
    OOPOP — copy R10 to R1
    OOPPN — copy R11 to R1
    OOPPO — copy R12 to R1
    OOPPP — copy R13 to R1

  - SK ttt skips one instruction depending on
    the sign of R1,R2,R3,R4 or the borrow/carry flag C:
    NPNNN - skip if R4 >= 0
    NPNNO - skip if R4 != 0
    NPNNP - skip if R4 <= 0
    NPNON - skip if R3 >= 0
    NPNOO - skip if R3 != 0
    NPNOP - skip if R3 <= 0
    NPNPN - skip if R2 >= 0
    NPNPO - skip if R2 != 0
    NPNPP - skip if R2 <= 0
    NPONN - skip if R1 >= 0
    NPONO - skip if R1 != 0
    NPONP - skip if R1 <= 0
    NPOON - skip if C == -1
    NPOOO - skip if C ==  0
    NPOOP - skip if C ==  1
    NPOPN - skip if R1 < 0
    NPOPO - skip if R1 == 0
    NPOPP - skip if R1 > 0
    NPPNN - skip if R2 < 0
    NPPNO - skip if R2 == 0
    NPPNP - skip if R2 > 0
    NPPON - skip if R3 < 0
    NPPOO - skip if R3 == 0
    NPPOP - skip if R3 > 0
    NPPPN - skip if R4 < 0
    NPPPO - skip if R4 == 0
    NPPPP - skip if R4 > 0