Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.3 alpha 4/15/85; site fear.UUCP Path: utzoo!watmath!clyde!burl!ulysses!bellcore!decvax!decwrl!amdcad!cae780!weitek!fear!mahar From: mahar@fear.UUCP (mahar) Newsgroups: net.arch Subject: Re: Re: Addressing modes Message-ID: <349@fear.UUCP> Date: Sun, 9-Mar-86 16:49:42 EST Article-I.D.: fear.349 Posted: Sun Mar 9 16:49:42 1986 Date-Received: Wed, 12-Mar-86 21:56:57 EST References: <187@anwar.UUCP> <1441@gitpyr.UUCP> <400@utastro.UUCP> <1441@wucec2.UUCP> Organization: Weitek Corp. Sunnyvale Ca. Lines: 35 > can get away with only one address. To wit: > > SUBS X Subtract cotents of location X from accumulator and > store results in accumulator and in X > > JUMP X Indirect jump; i.e. PC <= contents of location X > > Proving this beast to be functionally complete is arduous but do-able. > We use it as an exercise in our Computer Architecture class. The machine is > called the TWINC, for TWo INstruction Computer. We have surmised the existence > of an OINC, but have not successfully proved functional completeness (the > conditional branch is usually the problem). You describe OINC with two addr. - > can you do it with only one? Yes. The instruction is reverse subrtact and skip if borrow. There is no opcode field only the address field. The instruction subtracts the accumulator from the memory operand. The result is stored in both the accumulator and the memory operand and the next instruction is skipped if a borrow occured. Memory location 0 is the PC. A friend of mine built one of these out of TTL. He called it URISC for Ultimate Reduced Instruction Set Computer. It uses about 8 standard 7400 series TTL packages. In this implementation the PC went backwards but that is not necessary. He wrote a macro assembler which implemented a usable set of instructions. I know this design is functionally complete. I don't have a description with me, so I can't prove it now. If your really interested I can mail your a list of the macro package. -- Mike Mahar UUCP: {turtlevax, cae780}!weitek!mahar Disclaimer: The above opinions are, in fact, not opinions. They are facts.