Differences

The following table is an overview of all differences between the SYSTEM00, CDP1801 and CDP1802 instruction sets. Incompatible differences are shown with text in orange. The CDP1804 and CDP1805 (as well as CDP1806) have additional instructions starting with opcode 68.

Note that the SYSTEM00 is an implementation of the COSMAC instruction set likely constructed largely of 7400-series TTL logic, i.e. not a microprocessor. For more details on the SYSTEM00 see also Herb Johnson's page System 00 inspection. The 1801 is a 2-chip implementation which became the 1802.

This info is also available online on the Emma 02 site.

Opcode SYSTEM 00 CDP1801 CDP1802
00 IDLE R0 IDLE IDLE
0N (N<>0) IDLE RN undefined LDN RN
1N INC RN INC RN INC RN
2N DEC RN DEC RN DEC RN
30 BR xx BR xx BR xx
31 BNZ xx undefined BQ xx
32 BZ xx BZ xx BZ xx
33 BDF xx, BPZ xx or BGE xx BDF xx, BPZ xx or BGE xx BDF xx, BPZ xx or BGE xx
34 B1 xx B1 xx B1 xx
35 B2 xx B2 xx B2 xx
36 B3 xx B3 xx B3 xx
37 B4 xx B4 xx B4 xx
38 undefined SKP or NBR SKP or NBR
39 undefined undefined BNQ xx
3A undefined BNZ xx BNZ xx
3B undefined BNF xx, BM xx, BL xx BNF xx, BM xx, BL xx
3C undefined BN1 xx BN1 xx
3D undefined BN2 xx BN2 xx
3E undefined BN3 xx BN3 xx
3F undefined BN4 xx BN4 xx
4N LDA RN LDA RN LDA RN
5N STR RN STR RN STR RN
60 undefined OUT 0 IRX
6N (1 ≤ N ≤ 3) OUT N OUT N OUT N
6N (4 ≤ N ≤ 7) undefined OUT N OUT N
68 INP 0: BUS -> M(RX) INP 0: BUS -> M(RX) Reserved for 1804/1805
6N (9 ≤ N ≤ F) undefined INP N-8: BUS -> M(RX) INP N-8: BUS -> D, BUS -> M(RX)
70 RET RET RET
71 undefined DIS DIS
72 undefined undefined LDXA
73 undefined undefined STXD
74 undefined undefined ADC
75 undefined undefined SDB
76 undefined undefined SHRC or RSHR
77 undefined undefined SMB
78 SAV SAV SAV
79 undefined undefined MARK
7A undefined undefined REQ
7B undefined undefined SEQ
7C undefined undefined ADCI xx
7D undefined undefined SDBI xx
7E undefined undefined SHLC or RSHL
7F undefined undefined SMBI xx
8N GLO RN GLO RN GLO RN
9N GHI RN GHI RN GHI RN
AN PLO RN PLO RN PLO RN
BN PHI RN PHI RN PHI RN
C0 PHI R0 undefined LBR xxxx
C1 PHI R1 undefined LBQ xxxx
C2 PHI R2 undefined LBZ xxxx
C3 PHI R3 undefined LBDF xxxx
C4 PHI R4 undefined NOP
C5 PHI R5 undefined LSNQ
C6 PHI R6 undefined LSNZ
C7 PHI R7 undefined LSNF
C8 PHI R8 undefined LSKP or NLBR
C9 PHI R9 undefined LBNQ xxxx
CA PHI RA undefined LBNZ xxxx
CB PHI RB undefined LBNF xxxx
CC PHI RC undefined LSIE
CD PHI RD undefined LSQ
CE PHI RE undefined LSZ
CF PHI RF undefined LSDF
DN SEP RN SEP RN SEP RN
EN SEX RN SEX RN SEX RN
F0 LDX LDX LDX
F1 OR OR OR
F2 AND AND AND
F3 XOR XOR XOR
F4 ADD ADD ADD
F5 SD SD SD
F6 SHR SHR SHR
F7 undefined SM SM
F8 undefined LDI xx LDI xx
F9 undefined ORI xx ORI xx
FA undefined ANI xx ANI xx
FB undefined XRI xx XRI xx
FC undefined ADI xx ADI xx
FD undefined SDI xx SDI xx
FE undefined SHL SHL
FF undefined SMI xx SMI xx