ISA.md

DekatronPC Instruction set

DekatronPC Instruction set if fully compatible with brainfuck programming language, but have some extentions for maintance purposes.

In-memory representation for each instruction is 4-bit width, but there are two Instruction Set Registers - ISAR0 and ISAR1, which extend number of instructions from 16 to 64.

Brainfuck ISA (ISAR1=0, ISAR0=0)

Symbol	Opcode	Brainfuck	Name	Description
N	0x0		NOP	No instruction, can be used for alignment purposes
H	0x1		HALT	Stop machine execution, Namual resume
+	0x2	+	INC	Increment of Current data cell
-	0x3	-	DEC	Decrement of current data cell
>	0x4	>	AINC	Increment of address pointer
<	0x5	<	ADEC	Decrement of address pointer
[	0x6	[	LBEG	If current data cell equal zero, skip the loop
]	0x7	]	LEND	If current data cell not equal zero, repeat loop iteration
.	0x8	.	COUT	Print current symbol to the terminal
,	0x9	,	CIN	Read symbol from the terminal (Blocked acces - Program halted while no symbol)
R	0xA		RST	Hard reset
0	0xB		CLRD	Write zero to current Data Cell
3	0xC		ISA3	Set ISAR1 = 1 and ISAR0=1 - RESERVED ISA
P	0xD		ISA2	Set ISAR1 = 1 and ISAR0=0 - PunchTape ISA
M	0xE		ISA1	Set ISAR1 = 0 and ISAR0=1 - Maintaince ISA
B	0xF		ISA0	Set ISAR1 = 0 and ISAR0=0 - Brainfuck ISA (Default value)

Maintance ISA (ISAR1=0, ISAR0=1)

Symbol	Opcode	Brainfuck	Name	Description
	0x0
	0x1
	0x2
	0x3
>	0x4	>	AINC	Increment of address pointer
<	0x5	<	ADEC	Decrement of address pointer
{	0x6		LABEG	If current address equal zero, skip the loop
}	0x7		LAEND	If current address is not equal zero, repeat loop iteration
S	0x8		SETI	Set instruction counter to start point
I	0x9		CLRI	Clear instruction counter
A	0xA		CLRA	Clear address counter
0	0xB		CLRD	Clear Data
3	0xC		ISA3	Set ISAR1 = 1 and ISAR0=1 - RESERVED ISA
P	0xD		ISA2	Set ISAR1 = 1 and ISAR0=0 - PunchTape ISA
M	0xE		ISA1	Set ISAR1 = 0 and ISAR0=1 - Maintaince ISA
B	0xF		ISA0	Set ISAR1 = 0 and ISAR0=0 - Brainfuck ISA (Default value)

Bootloader

Bootloder is the code, which is performed after reset vector. In placed on the instruction address 0x00000;

Memory clearance routine

After Reset vector release we have zeroes in any counters, but memory can contain garbage. We need to do cleanup:

for (i = 0; i < 30000; ++i)
{
  Memory[i] = 0;
}

With Dekatron PC ISA we will get next code:

  MA0> //Select maintance ISA, Clear Address counter, Clear data and select next data cell
  {   // While address counter is not zero
    0 >//Cleanup current data cell and go next
  }
  B //Set Default brainfuck ISA