Altair 8800

Last Updated or created 2022-08-04

The Altair 8800 is a microcomputer designed in 1974 by MITS and based on the Intel 8080CPU. Interest grew quickly after it was featured on the cover of the January 1975 issue of Popular Electronics and was sold by mail order through advertisements there, in Radio-Electronics, and in other hobbyist magazines.

(picture from wikipedia)

UPDATE: 20220804 – Added Octal sheet

I alway loved the simple setup of this computer.
There was no screen and no keyboard.
Only later additions to the machine provided these.

One explanation of the Altair name, is that the name was inspired by Star Trek episode “Amok Time“, where the Enterprise crew went to Altair (Six).

There are only a few differences between the used 8080 CPU and the 8085 CPU of a machine i learned machinecode on.

See : https://www.henriaanstoot.nl/1989/01/01/8085-machinecode-at-school/

So for a really long time i wanted to have a Altair alike machine. There are do it yourself kits for sale. Which look like perfect relica’s and there are virtual machines and emulators. But i wanted to have the feeling of throwing the switches.
You can find a emulator here (https://s2js.com/altair/)

So i bought the components, a poker case which can hold the machine. And started building today.

The backend is a arduino based emulator, but with real leds and switches!
(https://create.arduino.cc/projecthub/david-hansel/arduino-altair-8800-simulator-3594a6)

Next to do:

  • Fix plate into case
  • Solder a LOT of wires and components!
    • Shall i get rid off the transitors and use darlington arrays?
  • Put lettering on the aluminium plate : Functions and Bus information.
  • Build a power connector in the case

And then … programming 🙂

UPDATE: 20220804 – Added Octal sheet

The Altair is a octal based machine, but i couldn’t find a opcode list in Octal. So i generated one.
When entering a MOV D,M instruction for example, you have to enter
x 0 1 0 1 0 1 1 0 using the switches
Thats 126 in octal but most tables are in hex ( MOV D,M is 56, which is 0101 0110 but not that clear on the switches)

Opcode (oct)InstructionfunctionsizeflagsOpcode
000NOP10x00
001LXI B,D16B <- byte 3, C <- byte 230x01
002STAX B(BC) <- A10x02
003INX BBC <- BC+110x03
004INR BB <- B+11Z, S, P, AC0x04
005DCR BB <- B-11Z, S, P, AC0x05
006MVI B, D8B <- byte 220x06
007RLCA = A << 1; bit 0 = prev bit 7; CY = prev bit 71CY0x07
0100x08
011DAD BHL = HL + BC1CY0x09
012LDAX BA <- (BC)10x0a
013DCX BBC = BC-110x0b
014INR CC <- C+11Z, S, P, AC0x0c
015DCR CC <-C-11Z, S, P, AC0x0d
016MVI C,D8C <- byte 220x0e
017RRCA = A >> 1; bit 7 = prev bit 0; CY = prev bit 01CY0x0f
0200x10
021LXI D,D16D <- byte 3, E <- byte 230x11
022STAX D(DE) <- A10x12
023INX DDE <- DE + 110x13
024INR DD <- D+11Z, S, P, AC0x14
025DCR DD <- D-11Z, S, P, AC0x15
026MVI D, D8D <- byte 220x16
027RALA = A << 1; bit 0 = prev CY; CY = prev bit 71CY0x17
0300x18
031DAD DHL = HL + DE1CY0x19
032LDAX DA <- (DE)10x1a
033DCX DDE = DE-110x1b
034INR EE <-E+11Z, S, P, AC0x1c
035DCR EE <- E-11Z, S, P, AC0x1d
036MVI E,D8E <- byte 220x1e
037RARA = A >> 1; bit 7 = prev bit 7; CY = prev bit 01CY0x1f
0400x20
041LXI H,D16H <- byte 3, L <- byte 230x21
042SHLD adr(adr) <-L; (adr+1)<-H30x22
043INX HHL <- HL + 110x23
044INR HH <- H+11Z, S, P, AC0x24
045DCR HH <- H-11Z, S, P, AC0x25
046MVI H,D8H <- byte 220x26
047DAAspecial10x27
0500x28
051DAD HHL = HL + HI1CY0x29
052LHLD adrL <- (adr); H<-(adr+1)30x2a
053DCX HHL = HL-110x2b
054INR LL <- L+11Z, S, P, AC0x2c
055DCR LL <- L-11Z, S, P, AC0x2d
056MVI L, D8L <- byte 220x2e
057CMAA <- !A10x2f
0600x30
061LXI SP, D16SP.hi <- byte 3, SP.lo <- byte 230x31
062STA adr(adr) <- A30x32
063INX SPSP = SP + 110x33
064INR M(HL) <- (HL)+11Z, S, P, AC0x34
065DCR M(HL) <- (HL)-11Z, S, P, AC0x35
066MVI M,D8(HL) <- byte 220x36
067STCCY = 11CY0x37
0700x38
071DAD SPHL = HL + SP1CY0x39
072LDA adrA <- (adr)30x3a
073DCX SPSP = SP-110x3b
074INR AA <- A+11Z, S, P, AC0x3c
075DCR AA <- A-11Z, S, P, AC0x3d
076MVI A,D8A <- byte 220x3e
077CMCCY=!CY1CY0x3f
100MOV B,BB <- B10x40
101MOV B,CB <- C10x41
102MOV B,DB <- D10x42
103MOV B,EB <- E10x43
104MOV B,HB <- H10x44
105MOV B,LB <- L10x45
106MOV B,MB <- (HL)10x46
107MOV B,AB <- A10x47
110MOV C,BC <- B10x48
111MOV C,CC <- C10x49
112MOV C,DC <- D10x4a
113MOV C,EC <- E10x4b
114MOV C,HC <- H10x4c
115MOV C,LC <- L10x4d
116MOV C,MC <- (HL)10x4e
117MOV C,AC <- A10x4f
120MOV D,BD <- B10x50
121MOV D,CD <- C10x51
122MOV D,DD <- D10x52
123MOV D,ED <- E10x53
124MOV D,HD <- H10x54
125MOV D,LD <- L10x55
126MOV D,MD <- (HL)10x56
127MOV D,AD <- A10x57
130MOV E,BE <- B10x58
131MOV E,CE <- C10x59
132MOV E,DE <- D10x5a
133MOV E,EE <- E10x5b
134MOV E,HE <- H10x5c
135MOV E,LE <- L10x5d
136MOV E,ME <- (HL)10x5e
137MOV E,AE <- A10x5f
140MOV H,BH <- B10x60
141MOV H,CH <- C10x61
142MOV H,DH <- D10x62
143MOV H,EH <- E10x63
144MOV H,HH <- H10x64
145MOV H,LH <- L10x65
146MOV H,MH <- (HL)10x66
147MOV H,AH <- A10x67
150MOV L,BL <- B10x68
151MOV L,CL <- C10x69
152MOV L,DL <- D10x6a
153MOV L,EL <- E10x6b
154MOV L,HL <- H10x6c
155MOV L,LL <- L10x6d
156MOV L,ML <- (HL)10x6e
157MOV L,AL <- A10x6f
160MOV M,B(HL) <- B10x70
161MOV M,C(HL) <- C10x71
162MOV M,D(HL) <- D10x72
163MOV M,E(HL) <- E10x73
164MOV M,H(HL) <- H10x74
165MOV M,L(HL) <- L10x75
166HLTspecial10x76
167MOV M,A(HL) <- A10x77
170MOV A,BA <- B10x78
171MOV A,CA <- C10x79
172MOV A,DA <- D10x7a
173MOV A,EA <- E10x7b
174MOV A,HA <- H10x7c
175MOV A,LA <- L10x7d
176MOV A,MA <- (HL)10x7e
177MOV A,AA <- A10x7f
200ADD BA <- A + B1Z, S, P, CY, AC0x80
201ADD CA <- A + C1Z, S, P, CY, AC0x81
202ADD DA <- A + D1Z, S, P, CY, AC0x82
203ADD EA <- A + E1Z, S, P, CY, AC0x83
204ADD HA <- A + H1Z, S, P, CY, AC0x84
205ADD LA <- A + L1Z, S, P, CY, AC0x85
206ADD MA <- A + (HL)1Z, S, P, CY, AC0x86
207ADD AA <- A + A1Z, S, P, CY, AC0x87
210ADC BA <- A + B + CY1Z, S, P, CY, AC0x88
211ADC CA <- A + C + CY1Z, S, P, CY, AC0x89
212ADC DA <- A + D + CY1Z, S, P, CY, AC0x8a
213ADC EA <- A + E + CY1Z, S, P, CY, AC0x8b
214ADC HA <- A + H + CY1Z, S, P, CY, AC0x8c
215ADC LA <- A + L + CY1Z, S, P, CY, AC0x8d
216ADC MA <- A + (HL) + CY1Z, S, P, CY, AC0x8e
217ADC AA <- A + A + CY1Z, S, P, CY, AC0x8f
220SUB BA <- A – B1Z, S, P, CY, AC0x90
221SUB CA <- A – C1Z, S, P, CY, AC0x91
222SUB DA <- A + D1Z, S, P, CY, AC0x92
223SUB EA <- A – E1Z, S, P, CY, AC0x93
224SUB HA <- A + H1Z, S, P, CY, AC0x94
225SUB LA <- A – L1Z, S, P, CY, AC0x95
226SUB MA <- A + (HL)1Z, S, P, CY, AC0x96
227SUB AA <- A – A1Z, S, P, CY, AC0x97
230SBB BA <- A – B – CY1Z, S, P, CY, AC0x98
231SBB CA <- A – C – CY1Z, S, P, CY, AC0x99
232SBB DA <- A – D – CY1Z, S, P, CY, AC0x9a
233SBB EA <- A – E – CY1Z, S, P, CY, AC0x9b
234SBB HA <- A – H – CY1Z, S, P, CY, AC0x9c
235SBB LA <- A – L – CY1Z, S, P, CY, AC0x9d
236SBB MA <- A – (HL) – CY1Z, S, P, CY, AC0x9e
237SBB AA <- A – A – CY1Z, S, P, CY, AC0x9f
240ANA BA <- A & B1Z, S, P, CY, AC0xa0
241ANA CA <- A & C1Z, S, P, CY, AC0xa1
242ANA DA <- A & D1Z, S, P, CY, AC0xa2
243ANA EA <- A & E1Z, S, P, CY, AC0xa3
244ANA HA <- A & H1Z, S, P, CY, AC0xa4
245ANA LA <- A & L1Z, S, P, CY, AC0xa5
246ANA MA <- A & (HL)1Z, S, P, CY, AC0xa6
247ANA AA <- A & A1Z, S, P, CY, AC0xa7
250XRA BA <- A ^ B1Z, S, P, CY, AC0xa8
251XRA CA <- A ^ C1Z, S, P, CY, AC0xa9
252XRA DA <- A ^ D1Z, S, P, CY, AC0xaa
253XRA EA <- A ^ E1Z, S, P, CY, AC0xab
254XRA HA <- A ^ H1Z, S, P, CY, AC0xac
255XRA LA <- A ^ L1Z, S, P, CY, AC0xad
256XRA MA <- A ^ (HL)1Z, S, P, CY, AC0xae
257XRA AA <- A ^ A1Z, S, P, CY, AC0xaf
260ORA BA <- A | B1Z, S, P, CY, AC0xb0
261ORA CA <- A | C1Z, S, P, CY, AC0xb1
262ORA DA <- A | D1Z, S, P, CY, AC0xb2
263ORA EA <- A | E1Z, S, P, CY, AC0xb3
264ORA HA <- A | H1Z, S, P, CY, AC0xb4
265ORA LA <- A | L1Z, S, P, CY, AC0xb5
266ORA MA <- A | (HL)1Z, S, P, CY, AC0xb6
267ORA AA <- A | A1Z, S, P, CY, AC0xb7
270CMP BA – B1Z, S, P, CY, AC0xb8
271CMP CA – C1Z, S, P, CY, AC0xb9
272CMP DA – D1Z, S, P, CY, AC0xba
273CMP EA – E1Z, S, P, CY, AC0xbb
274CMP HA – H1Z, S, P, CY, AC0xbc
275CMP LA – L1Z, S, P, CY, AC0xbd
276CMP MA – (HL)1Z, S, P, CY, AC0xbe
277CMP AA – A1Z, S, P, CY, AC0xbf
300RNZif NZ, RET10xc0
301POP BC <- (sp); B <- (sp+1); sp <- sp+210xc1
302JNZ adrif NZ, PC <- adr30xc2
303JMP adrPC <= adr30xc3
304CNZ adrif NZ, CALL adr30xc4
305PUSH B(sp-2)<-C; (sp-1)<-B; sp <- sp – 210xc5
306ADI D8A <- A + byte2Z, S, P, CY, AC0xc6
307RST 0CALL $010xc7
310RZif Z, RET10xc8
311RETPC.lo <- (sp); PC.hi<-(sp+1); SP <- SP+210xc9
312JZ adrif Z, PC <- adr30xca
3130xcb
314CZ adrif Z, CALL adr30xcc
315CALL adr(SP-1)<-PC.hi;(SP-2)<-PC.lo;SP<-SP-2;PC=adr30xcd
316ACI D8A <- A + data + CY2Z, S, P, CY, AC0xce
317RST 1CALL $810xcf
320RNCif NCY, RET10xd0
321POP DE <- (sp); D <- (sp+1); sp <- sp+210xd1
322JNC adrif NCY, PC<-adr30xd2
323OUT D8special20xd3
324CNC adrif NCY, CALL adr30xd4
325PUSH D(sp-2)<-E; (sp-1)<-D; sp <- sp – 210xd5
326SUI D8A <- A – data2Z, S, P, CY, AC0xd6
327RST 2CALL $1010xd7
330RCif CY, RET10xd8
3310xd9
332JC adrif CY, PC<-adr30xda
333IN D8special20xdb
334CC adrif CY, CALL adr30xdc
3350xdd
336SBI D8A <- A – data – CY2Z, S, P, CY, AC0xde
337RST 3CALL $1810xdf
340RPOif PO, RET10xe0
341POP HL <- (sp); H <- (sp+1); sp <- sp+210xe1
342JPO adrif PO, PC <- adr30xe2
343XTHLL <-> (SP); H <-> (SP+1)10xe3
344CPO adrif PO, CALL adr30xe4
345PUSH H(sp-2)<-L; (sp-1)<-H; sp <- sp – 210xe5
346ANI D8A <- A & data2Z, S, P, CY, AC0xe6
347RST 4CALL $2010xe7
350RPEif PE, RET10xe8
351PCHLPC.hi <- H; PC.lo <- L10xe9
352JPE adrif PE, PC <- adr30xea
353XCHGH <-> D; L <-> E10xeb
354CPE adrif PE, CALL adr30xec
3550xed
356XRI D8A <- A ^ data2Z, S, P, CY, AC0xee
357RST 5CALL $2810xef
360RPif P, RET10xf0
361POP PSWflags <- (sp); A <- (sp+1); sp <- sp+210xf1
362JP adrif P=1 PC <- adr30xf2
363DIspecial10xf3
364CP adrif P, PC <- adr30xf4
365PUSH PSW(sp-2)<-flags; (sp-1)<-A; sp <- sp – 210xf5
366ORI D8A <- A | data2Z, S, P, CY, AC0xf6
367RST 6CALL $3010xf7
370RMif M, RET10xf8
371SPHLSP=HL10xf9
372JM adrif M, PC <- adr30xfa
373EIspecial10xfb
374CM adrif M, CALL adr30xfc
3750xfd
376CPI D8A – data2Z, S, P, CY, AC0xfe
377RST 7CALL $3810xff
Spread the love