Simple 8Bit Accumulator+Stack Computer
author Neil Franklin, last modification 2005.02.26

Inmos T212 like
but with 8bit ALU and accumulator (no internal stack) and external stack
  no internal stack, instead just accumulator + 1 16bit base reg for addressing
    in this respect if follows the 6800 for its relatively small abilities

PC(16)
SP/WP(16)
Acc(8)
Base(16)
Opr(4|12)

instr 8bit, 4+4, 12..15 const instr, [1..4]*16 non-const instr
  no evaluation of OPR register for non-const instr, unless very easy
on-stack local vars are very fast, global stuff only by base+offset/index
  globals need reloading base for multiple array, already 6 or 16 instr
    so only one base register, do load/store 8-er packs to/from stack

LDO (load opr) 1 or 3 times each 4 bits, together with instr 4 bits
LDN (load negative opr) 1 time, then 1 or 2 LDO, together with instr 4 bits

LDC (load const 8bit) to A

LDA (load stack sp+8|16) to A
STA (store stack sp+8|16) from A

SEB (set base) from stack+8|16
SVB (save base) to stack+8|16
LDB (load base+8|16) to A
STB (store base+8|16) from A
LDI (load base incrementing, non-const) to A
STI (store base incrementing, non-const) from A

JMP (jump pc+16)
JSR (jump subroutine pc+16)
or JAL (jump and link pc+16)
CJP (calculated jump sp+8|16)
BRZ (branch zero pc+16)

SAJ (stack adjust) sp+8|16)