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Questions tagged [8088]

For questions specifically regarding the Intel 8088 microprocessor.

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12 votes
3 answers
2k views

What is the technical definition of "clone" that makes the K1810VM88 (К1810ВМ88) not a clone of the 8088?

The Clueless Engineer YouTube channel posted a video yesterday exploring a Soviet K1810VM88 CPU he got from Ukraine. Apparently he originally used the wording in the video title that the K1810VM88 was ...
hippietrail's user avatar
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4 votes
1 answer
193 views

8251A UART outputs unexpected data

I am currently prototyping an Intel 8088 system (Maximum Mode) on a breadboard. Later I want to move to custom designed PCB. To get some input and output, I wanted to use the 8251A chip. I have two ...
x95's user avatar
  • 151
14 votes
3 answers
2k views

Help porting nasm code down from 386 to 8088 (shifts by more than 1 bit)

I have been writing some small asm COM program using Netwide Assembler (nasm), but am having trouble getting it to run on 8088 emulators like PCjs. I could use some help translating the assembly "...
don bright's user avatar
0 votes
2 answers
358 views

Difference between the 8255 and 8042 PPIs

What is the big difference between the 8255 PPI and the 8042 PPI? (except that the 8255 has more IO) Things that I spotted: the 8042 seems to have its own clock (not using the CPU one) which seems to ...
juffma's user avatar
  • 195
13 votes
2 answers
2k views

Intel 80188 & 8087 clock frequency differences

Today I saw that the Intel APX-188/186 User's Manual states that you can use a 8087 as coprocessor for the 80188/186 (as the 80187 is only usable with the 186). But I was wondering about the clock ...
juffma's user avatar
  • 195
4 votes
1 answer
238 views

Are there multiple models of the Intel 8089 IOP?

As far as I'm concerned there is only one model of the Intel 8089 (the D8089A-3). I am not able to find any information on this. While the 8086,8088 and 8087 use the scheme of the last number (-3 in ...
juffma's user avatar
  • 195
-4 votes
1 answer
388 views

What is the fastest 8088-compatible machine? [closed]

I can see a PC benchmark sheet here. It shows that the fastest XT is Juko XT, which runs at 12 MHz with NEC V20. I actually own one, and I've checked that it runs at 12 MHz. But another thing I know ...
Sung's user avatar
  • 389
11 votes
2 answers
702 views

When 8086 and 8088 actually sample READY to determine if wait states need to be inserted?

Just for hobby and research purposes I design an XT compatible machine based on 8086, and now I have to come up with a wait state generator for IO devices that are slow and require additional time to ...
Linol's user avatar
  • 113
1 vote
1 answer
430 views

8088 CPU A16-A19 address lines go crazy with nop test after 0FFFF address

I'm building a minimal, minimum mode 8088 computer. I started with an 80C88-2 (CMOS, static variant) CPU. My configuration is really simple. One CPU, one 74HCT245 (DTR->DT/R) for the data lines, ...
Pethical's user avatar
  • 133
15 votes
2 answers
3k views

Why did the 8087 need a special socket?

The IBM PC included a coprocessor socket for the 8087 floating-point unit. Logical enough; some customers wanted to use the 8087 to make numeric calculations run faster. But why was the 8087 designed ...
rwallace's user avatar
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10 votes
2 answers
978 views

Did any 8-bit CPUs use dynamic memory for registers?

According to https://jamiestarling.com/project-8088-the-8088-cpu-pinout/ One thing to note – the 8088 registers are made from dynamic memory cells – they have to be refreshed. The minimum clock speed ...
rwallace's user avatar
  • 61.2k
3 votes
0 answers
151 views

Zenith Data Systems laptop with Timer Interrupt Error

I have an old Zenith “laptop” that runs on an 80c88 processor, and apparently was manufactured around 1985. It’s quite a beast of a laptop - size and weight, rather than computing power!. ...
RobC's user avatar
  • 99
35 votes
4 answers
9k views

How much did IBM save by limiting the PC to 4.77 MHz?

My understanding is the CPU clock speed on the Intel 8088 in the IBM PC was selected as 4.77 MHz to simplify the design of the system. This despite the 8088 coming in two versions - 5 MHz and 8 MHz. ...
Brian H's user avatar
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10 votes
3 answers
2k views

Did multiplexed address/data lines make memory access slower?

Looking at the pinout of e.g. the 8088, it multiplexes the data lines onto eight of the address lines; presumably the designers judged that being able to squeeze the chip into a 40-pin package, would ...
rwallace's user avatar
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5 votes
3 answers
1k views

Need circuit - manual step-by-step clock for 8086/8088

I finally bought a ceramic 8086-1 (from ebay, from China - I'm not sure that it is not fake chip) and 8284 (it make the necessary synchronization signal for the processor from the crystal). Now I ...
Alex's user avatar
  • 471
21 votes
4 answers
2k views

Did the IBM PC use the 8088's NMI line?

As I understand it, the Intel 8088 CPU used in the original IBM PC had two interrupt lines: INTR and NMI. INTR was fed from the Intel 8259 Programmable Interrupt Controller, which handled the IRQs ...
smitelli's user avatar
  • 1,769
2 votes
2 answers
519 views

Will the circuit work normally if different chip speeds (eg 8088-2 and 8255-1)

Old processors came out with support chips. That is, there was a family - the processor and its chips. Over time, the same kits came out with higher frequencies. Will the circuit work properly if ...
Alex's user avatar
  • 471
52 votes
4 answers
12k views

What did the 8086 (and 8088) do upon encountering an illegal instruction?

Preface: This question does in part intersect with Use of undocumented opcodes, but targets especially the 8086 instruction handling. I was reading Tanenbaum's "Operating Systems, Design and ...
Joe D's user avatar
  • 631
7 votes
2 answers
2k views

IBM PC memory map - why RAM at the bottom?

The 8088 provided an address space of one megabyte. The IBM PC allocated that address space as 640K RAM (not that the 5150 could physically take that much, but the address space was allocated) ...
rwallace's user avatar
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12 votes
3 answers
986 views

How to keep the instruction prefetcher filled up

My understanding is that the Intel 8088 has this buffer which reads ahead in the instruction stream whenever it has a spare bus cycle or two, so that when the time comes to execute that instruction, ...
Omar and Lorraine's user avatar
10 votes
2 answers
812 views

8086 pinout and address space limit

It is tempting to say - and I have said - that Intel made a mistake in the design of the 8086 and 8088, in going from 16 bit addresses to only 20 bits; if they had even shifted the segment registers ...
rwallace's user avatar
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9 votes
3 answers
2k views

Do I have to use an 8284 chip with the 8088?

I recently got the idea to start an 8088 system because I've been really interested in retro computing and the idea of a "breadboard computer" sounds very fun. From what I've read, every homebrew ...
DylanG's user avatar
  • 91
5 votes
2 answers
3k views

Why the "jmp" instruction is not working?

I have written the following program in debug.exe: 1165:0100 mov ah, 09 1165:0102 mov dx, 107 1165:0105 int 21 1165:0107 db 'Hello World', 0A, 0D, '$' 1165:0115 jmp 1165:0100 However, when I ...
user5161's user avatar
  • 475
16 votes
4 answers
3k views

Did the Intel 8086/8088 not guarantee the value of SS:SP immediately after RESET?

I'm poking at the Intel 8086/8088 (iAPX 86/88) User's Manual, which states on page 2-29 (PDF page 48), table 2-4, CPU State Following RESET, that the state of the CPU after the RESET pin rising ...
user's user avatar
  • 5,296
36 votes
4 answers
7k views

What was the IBM PC cost saving for using the 8088 vs 8086?

The decision to use the 8088, a version of the 8086 with the data bus restricted to 8 bits, in the original IBM PC, seems strange on the face of it, certainly hurt performance and intuitively shouldn'...
rwallace's user avatar
  • 61.2k