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20 votes
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How does the 8086 jump instruction work when the target address overflows?

Most of the time on x86, you have to consider segments and offsets separately. Opcode 0xE9 is a near jump, it only touches IP. The addition wraps around, so the target is the relative offset (as a ...
Stephen Kitt's user avatar
10 votes

1984 accounting software running in VirtualBox fails to print property to an LPT passthrough, but other software seems fine

Back in the 1970s, as a college project, I wrote an emulator for a minicomputer (in Fortran (!!)). When my professor ran a program written for the minicomputer, the teletype output was doubled, ...
DoxyLover's user avatar
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9 votes

1984 accounting software running in VirtualBox fails to print property to an LPT passthrough, but other software seems fine

Back in the early 1980s, some applications would operate the printer port hardware directly, not going through DOS or BIOS. I'm suspicious that Virtual Box is emulating the hardware, but being fooled ...
John Dallman's user avatar
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9 votes

What do the pins D0-D7 on the Intel 8080 exactly signify?

Basics The data bus carries time multiplexed information: At the end of the first clock cycle (*1) of each machine cycle (*2) it always carries the status signals as described on Page 2-6. During the ...
Raffzahn's user avatar
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9 votes
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Z80 to 68000 translator for CP/M

TL;DR: Early on the user side need was covered by hardware add on, as software couldn't deliver, while later on (>1985) no market existed to pay for such a product. CP/M was mostly portable across ...
Raffzahn's user avatar
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6 votes
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Understanding the Need for Positive Sync Polarities in Sony PVM Monitors

Summary Do not connect H-sync and V-sync outputs together with a T-connector! (See below for more details.) Your Sony PVM requires negative-going composite sync, and positive-going sync will probably ...
cjs's user avatar
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5 votes

Z80 to 68000 translator for CP/M

In addition to issues with self-modifying code, many instructions on the 68000 affect flags differently from their Z80 counterparts. If a Z80 program does something like: ADD B LD B,A LD ...
supercat's user avatar
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4 votes

Z80 to 68000 translator for CP/M

What prevented, at least on more powerful 68000 and 8086 systems, the creation of a loader that translated z80 instructions in native machine language? Any machine from that period with 128kb of RAM ...
Kuba hasn't forgotten Monica's user avatar
3 votes

How does the 8086 jump instruction work when the target address overflows?

I am absolutely not an expert on x86 bare-metal stuff (I play in the 8-bit era) but I've read enough over the years for this to set my A20 spidey-sense tingling. Is this the wrap-around behavior of ...
Eight-Bit Guru's user avatar
3 votes

Understanding the Need for Positive Sync Polarities in Sony PVM Monitors

The service manual says the monitor has external sync defined as negative polarity, as expected from composite sync signals for standard 525/625 line TV scan systems, either from composite video input,...
Justme's user avatar
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3 votes

Understanding the Need for Positive Sync Polarities in Sony PVM Monitors

In older VGA monitors, both hsync and vsync polarity tells the monitor which size it has to zoom vertically. If you use the wrong combined sync polarity for a given vertical resolution the picture is ...
Janka's user avatar
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3 votes

How to keep running DOS 16 bit applications when Windows 11 drops NTVDM

There is another software solution not mentioned in the existing answers: winevdm. It's supposed to be a drop-in replacement for the old NTVDM that works on x64 Windows. It hooks itself in the native ...
zdimension's user avatar
2 votes

Is there a C64(or any other) emulation that can be run in terminal?

"or any other emulator" would include emulators like SIMH that are meant to emulate old mainframe/minicomputer systems that were supposed to be used with literal terminals - these will ...
rackandboneman's user avatar

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