Questions tagged [8088]
For questions specifically regarding the Intel 8088 microprocessor.
17
questions
1
vote
1answer
280 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, ...
16
votes
2answers
2k 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 ...
10
votes
2answers
800 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 ...
3
votes
0answers
115 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!.
...
34
votes
4answers
8k 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. ...
9
votes
3answers
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 ...
5
votes
3answers
893 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 ...
19
votes
4answers
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 ...
2
votes
2answers
387 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 ...
49
votes
4answers
11k 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 ...
4
votes
2answers
1k 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) ...
11
votes
3answers
826 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, ...
9
votes
2answers
671 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 ...
9
votes
3answers
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 ...
5
votes
2answers
2k 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 ...
15
votes
4answers
2k 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 ...
34
votes
4answers
6k 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'...