For questions about the Intel 8080 8-bit microprocessor
For questions specifically regarding the 8080 processor, manufactured by Intel.
Related tags and processors:
Questions tagged [8080]
75 questions
20
votes
3 answers
How does this 8080 code perform division with remainder?
Empirically, I've found that this routine (i8080) divides value from E by B and returns the result in D and E (result and remainder of division).
divide_by_12_with_rest:
MVI C, 9 ; @1
MOV A, D ; @2
loop_1:
MOV D, A ; @3
MOV A, E
RAL
…
DraganS
- 353
- 2
- 9
20
votes
3 answers
Bit one of the Intel 8080's Flags register
Did bit one of the Intel 8080's Flags register, the bit between the carry and parity flags, get set to one on startup? If so what was the reason for this, and was this inherited from the 8008 Flags register?
Single Malt
- 1,839
- 1
- 7
- 28
14
votes
4 answers
Why do the i8080 I/O instructions take a byte-sized operand to determine the port?
I thought the i8080 had 8 16-bit IN ports and 8 16-bit OUT ports. Doesn't that mean the instructions
IN d8 ; only index 0-7?
OUT d8
can only take 8 possible values? What would it be indexing otherwise?
dav
- 1,059
- 1
- 10
- 16
13
votes
4 answers
In the Intel 8080, where does the "Stack" start?
Having trouble trying to search for this in the data sheet, just have seen how big it is and how it handles stack pointers. Would anyone mind helping me out where the "Stack" start on an Intel 8080?
Ssweet-disposition
- 139
- 1
- 3
12
votes
1 answer
What is the difference between i8080 and i8080a?
There is some info over the net regarding 'some i8080 bugs were fixed in i8080a', but the exact bugs and differences are not usually disclosed. So, what is the exact difference between i8080 and i8080a?
lvd
- 10,382
- 24
- 62
12
votes
1 answer
The behavior of the auxiliary carry flag in subtraction on Intel 8080
Does SUB B on Intel 8080 set the auxiliary carry flag when the accumulator and the B register are 1 and 0, respectively? On Z80, which was designed to be a backward-compatible, albeit not fully, extension to 8080, the half-carry flag is defined so…
user5583413
- 123
- 6
10
votes
1 answer
Why was the 8080's JumP immediate instruction placed where it was?
On the 8080 there are many instructions with parallel forms. Three of these are CALL, RET and JP, which all have conditional and immediate forms.
Note: I am using Z80 terminology because that is what I am familiar with.
In octal:
3p0 - RET …
CJ Dennis
- 2,517
- 1
- 15
- 30
5
votes
0 answers
Manual for DIAGNOSTICS II V1.2 – CPU TEST SUPERSOFT ASSOCIATES
I am building a 8080 emulator. I found some useful test suites here. The emulator passes the first test suite (8080/8085 CPU Diagnostic, version 1.0, by Microcosm Associates), but not the second (DIAGNOSTICS II V1.2 – CPU TEST SUPERSOFT…
EL Dendo
- 1,112
- 6
- 10
3
votes
3 answers
Did the original Intel peripherals use latches as input registers?
This is more a question to satisfy my curiosity.
When looking at the original timing diagrams for reading and writing (e.g. for the 8255 and the 8250), these signals are never expressed in function of a clock. The 8255 doesn't even have a clock…
chthon
- 700
- 2
- 6
- 18
2
votes
1 answer
Auxiliary Carry and the Intel 8080's logical instructions
I'm trying to figure out how the Auxiliary Carry flag on the 8080 is affected by logical instructions.
Reading the Intel 8080 manual, it seems that logical instructions do not affect AC:
The Auxiliary Carry bit will be affected by all addition,…
tobiasvl
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