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