According to the CP/M FAQ and the Wikipedia entry, the Z800 was the planned NMOS version of what later became the CMOS Z280.

The R800 Wikipedia entry says that the R800 was based on the Z800, but based on the Z80 instruction set. The documents in r800.zip at z80.info (local copy) list the R800 instruction set, showing it to be exactly the same as the Z80, with the addition of the Z280's MULT A,r and MULT HL,rr instructions, and the unofficial SLS changed to TST:

R800 changed opcodes over Z80:

      Z80 intruction    R800 instruction
CB 30 SLS B             TST B
CB 31 SLS C             TST C
CB 32 SLS D             TST D
CB 33 SLS E             TST E
CB 34 SLS H             TST H
CB 35 SLS L             TST L
CB 36 SLS (HL)          TST (HL)
CB 37 SLS A             TST A

R800 additional opcodes over Z80:

ED C1 MULTU A,B            ED C3 MULTU HL,BC
ED C9 MULTU A,C
ED D1 MULTU A,D            ED D3 MULTU HL,DE
ED D9 MULTU A,E
ED E1 MULTU A,H            ED E3 MULTU HL,HL
ED E9 MULTU A,L
ED D1 MULTU A,(HL)         ED F3 MULTU HL,SP
ED D9 MULTU A,A

---

Hosted by Force9 Internet - Authored by J.G.Harston
Last update: 04-Jul-2008