Questions tagged [8085]

For questions about the 8085 8-bit microprocessor

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6 votes
1 answer

Why did the 8085 multiplex data with the low address byte?

Intel’s 8085 used bus multiplexing to stuff more functionality into 40 pins than would otherwise be possible. One of those pins, ALE, signals when the AD0…7 pins are outputting the low byte of the ...
  • 2,110
10 votes
2 answers

Simulating a 8085 using a Z80?

I am studying the replacement of a 8085 with a Z80 (I am aware that they are not pin-compatible, the solution is to be made in a board of new design rather than on the old board). The sole reason is ...
21 votes
3 answers

Z80 to x86 asm translator?

8086 is source code compatible with 8080. Zilog Z80 extended Intel 8080 with: An enhanced instruction set including bit manipulation, block move, block I/O, and byte search instructions New IX and IY ...
  • 3,118
2 votes
1 answer

Execution time for conditional jumps on the Intel 8080

On the Intel 8080, all conditional instructions have varying execution time depending on whether the condition is true or not, except conditional jumps. Why is this? The Intel 8085 changes this; there,...
  • 1,429
18 votes
1 answer

Which undocumented 8085 instructions is Steven Morse referring to in "In The Beginning"?

In S. P. Morse's 1980 allegory, "In The Beginning", he writes And Intel said, "Let there be an 8085 with an oscillator on the same chip as the processor, and let an on-chip system controller ...
  • 3,268
3 votes
1 answer

Carry flag in 8080/8085 subtraction

How is the carry flag set during a subtraction by the 8080 or 8085 processor? For addition, the carry flag is set if the result is greater than 255 (i.e. if it overflows). From the programmer's ...
  • 1,965
11 votes
1 answer

8080/8085 Instruction Test Suite

(This question was inspired by Comprehensive test suites for MOS 6520 PIA / 6522 VIA / 6526 CIA) Is there a comprehensive test suite for the Intel 808X series of processors? Something that would ...
  • 9,322
8 votes
2 answers

Intel 8080 Read/Set Interrupt Mask Instructions

According to Intel's 8080-8085 Assembly Language Programming guide, the OP Code 20 corresponds to the Read Interrupt Mask (RIM) instruction, and 30 corresponds to the Set Interrupt Mask (SIM) ...
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