NoRAL description

No-Register Assembly Language

General Concept
An extremely minimal assembly language based on a hypothetical processor with no internal registers.
All memory is external to the processor
Addresses are 16 bit, stored big endian
Memory is 8 bits
Instructions use 0, 1, or 2 memory references
m1 - first memory reference, updated with result of operation
m2 - second memory reference
xxx m1 m2 - 3 letter mnemonic separated with spaces
Program listings are understood to be in hex
It’s okay to write self-modifying code (maybe even necessary)
# comment with ‘#’ as first character in a line


Addressing Modes
Implied  : (brk, nop, ret)
Absolute : 2 byte address, 10f0 (14 other instructions)
Immediate: 1 byte, 2a: (sto)

Memory:                  0000 - ffff
Program Counter:         0000 - 0001   (initialized to 0200)
Carry Flag:              0002
Zero Flag:               0003
Top of Stack             0004
Stack                    0005 - 00ff
Display Memory:          0100 - 01ff, 32 x 8, 256 bytes
Start of program memory: 0200

Instructions

Op Code		Mnemonic		Example			Description (flags affected)
00			brk				brk				Halt program (none)
01			add				add 110a 2f00	m1 = m1 + m2 (CZ)
02			and				and dead beef	m1 = m1 & m2 (Z)
03			jmp				jmp 100f		program counter = m1 (none)
04			jpc				jpc 0600		if Carry flag = 1: PC = m1 (none)
05			jpz				jpz 070e		if Zero flag = 1: PC = m1 (none)
06			jsr				jsr 20a0		push PC, inc Top of stack, PC = m1 (none)
07			mov				mov 0616 b00b	m1 = m2 (Z)
08			nop				nop				place holder (none)
09			not				not 04ed		m1 = not m1 (Z)
0a			orr				orr de05 de80	m1 = m1 | m2 (Z)
0b			pop				pop 1100		pop top of stack into m1 (none)
0c			psh				psh 1100		push m2 onto top of stack (none)
0d			ret				ret				pop PC from stack (none)
oe			shl				shl 3c07		shift bits left: C<7<6<5<4<3<2<1<0<zero (C)
0f			shr				shr 3c07		shift bits right: zero>7>6>5>4>3>2>1>C (C)
10			sto				sto 3c07 33		store m1 with m2(immediate) (Z)
11			sub				sub de05 de80	m1 = m1 - m2 (CZ)
12			inc				inc 1000		m1 += 1 (CZ)
13			dec				dec 1000		m1 -= 1 (CZ)


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