ternary

# Ternary CPU

Balanced ternary trits of `-`, `0` and `+`

1 tribble = 6 trits (729 states)

CPU memory map addresses are 1 tribble (------ to ++++++), operations operate on tribbles

Three special registers (p = program counter, s = stack pointer, q = query processor)

Three general registers (a, x, y)



## Memory map

### ------ to -+++++: RAM (3^5 = 243 addresses = 177147 states)

* ------ upwards: Heap
* -+++++ downwards: Stack

### 0----- to 0--+++: IO (3^3 = 27 addresses = 19683 states)

### 0-0--- to 0+++++: Reserved (2 * 3^4 = 162 addresses = 118098 states)

### +----- to ++++++: ROM (3^5 = 243 addresses = 177147 states)



## Registers

### p: Program counter

6-trit register holding the address of the next instruction to be executed.


### q: Query processor

6-trit stateholder register states:

* .....-: carry
* .....+: overflow
* ....-.: negative
* ....+.: zero
* ...X..: compare
* XXX...: reserved


### s: Stack pointer

The stack shares memory locations ------ to -+++++ with the heap. 

The stack pointer is a 6-trit (5 absolute, 1 state) register serving as negative offset from -+++++.

IDEA: Three pointers from state trit.


### x|y|z: General purpose



## Instructions

Asterisk next to size indicates redundant instruction

Sz  Instr     Result

2   add 13 x
2*  add 13 y
2*  add 13 z
1*  add x x
1   add x y
1*  add x z
1*  add y x
1*  add y y
1   add y z
1   add z x
1*  add z y
1*  add z z
2   add &13 x
2*  add &13 y
2*  add &13 z
1*  add &x x
1   add &x y
1*  add &x z
1*  add &y x
1   add &y y
1*  add &y z
1*  add &z x
1   add &z y
1*  add &z z
--|repeat for all binary operations|--
* nand: logic building block
* bne: operands are offsets for compare flag of - and of +
* cmp: alpha < beta ? - : alpha > beta ? + : 0
* mov: beta := alpha
* ld: load tribble into register
* st: store tribble into register

Sz  Instr
1   clr x
1*  clr y
1*  clr z
1*  clr p
1*  clr q
1*  clr s

1*  jmp 13
1   jmp x
1*  jmp y
1*  jmp z
1*  jmp p
1*  jmp q
1*  jmp s
1*  jmp &13
1   jmp &x
1*  jmp &y
1*  jmp &z
1*  jmp &p
1*  jmp &q
1*  jmp &s
--|repeat for all unary operations|--
* psh: push alpha onto stack
* pop: pop alpha off stack

1   nop




## Septemvigesimal numeral system

--- = a
--0 = b
--+ = c
-0- = d
-00 = e
-0+ = f
-+- = g
-+0 = h
-++ = i
0-- = 1
0-0 = 2
0-+ = 3
00- = 4
000 = 5
00+ = 6
0+- = 7
0+0 = 8
0++ = 9
+-- = A
+-0 = B
+-+ = C
+0- = D
+00 = E
+0+ = F
++- = G
++0 = H
+++ = I