Instruction Set

The b16 Processor is a minimalistic stack processor, inspired by Chuck Moore's recent work. The original incarnation is 16 bit, byte addressed. There are 32 instructions, each is 5 bits. Three and a bit (literally!) are packed into a 16 bit word (bundle). The first slot in the bundle can only be a nop or a call.

	0	1	2	3	4	5	6	7	Comment
0	nop	call	jmp	ret	jz	jnz	jc	jnc	destination in rest of instruction
	nop	exec	goto	ret	gz	gnz	gc	gnc	for slot 3
8	xor	com	and	or	`+`	`+c`	`*+`	`/-`
10	A!+	A@+	R@+	lit	Ac!+	Ac@+	Rc@+	litc
	A!	A@	R@	lit	Ac!	Ac@	Rc@	litc	for slot 1
18	nip	drop	over	dup	>r	>a	r>	a

Purpose

The b16 is intented as small microcontroller, and suitable if you need more processing power than a 8051, but less die space (or gate count) and power consumption.

Documentation

You can find more documentation in the Forth Tagung 2002 presentation (131k), or the English translation (123k). There's also a combined presentation from 2005 (360k).

News

There's now a USB interface (not fully tested, undocumented), minimalistic interrupts (tested, somewhat documented), and a small test bench to integrate all that stuff. I plan to also add an Ethernet MAC, and build a new Cyclone-based board with both USB and Ethernet functionality.

b16-small

The small version of the b16 has an even further reduced instruction set, and fits into half the size.

	0	1	2	3	4	5	6	7	Comment
0	nop	call	jmp	ret	jz	jnz	jc	jnc	destination in rest of instruction
	nop	exec	goto	ret	gz	gnz	gc	gnc	for slot 3
8	xor	com	and	or	`+`	`+c`	`2/`	`c2/`
10	!+	@+	@	lit	c!+	c@+	c@	litc
	!.	@.	@	lit	c!.	c@.	c@	litc	for slot 1
18	nip	drop	over	dup	>r	nop	r>	nop

Download

You can download the Sources (143k) here. A more recent version is in the git repository, you can download it as follows from github or gitlab:

git clone https://github.com/forthy42/b16-small.git

git clone https://gitlab.com/forthy42/b16-small.git