Computer with 8051 z VGA by piotr_go

piotr_go 09 Nov 2019 13:46 Cool? (+54)

Recently, while browsing the archive with my old projects, I found a project that for ~ 20 years did not get a decent plate. It was designed, but I didn't really feel like it or had the skills (2 layers) to make it. As the project was quite interesting, I decided to dig it out.
It is a computer project based on the 8051 microcontroller. Originally there were several versions: with RS232, with text LCD, with remote control, with AT keyboard, and with WAV, MIDI, MP3 ... ADC playback modules for playing with audio. Programs could be loaded from disk or via RS232. There was a HEX editor. Everything written in assembler (that I also wanted ...

).
There was nothing to modify the original files (Protel hehe), so I designed the tiles in a different software.

The presented version of the computer has:
- CPU AT89LP51
- 128KB of ram
- 82C55 IO
- ATA controller
- 8bit DAC
- 80x40 text terminal with PS / 2 keyboard

16V8 serves as an address decoder:
Program memory 0x0000 ... 0xFFFF = 0x00000 ... 0x0FFFF SRAM
Data memory 0x0000 ... 0x007F = 82C55
Data memory 0x0080 ... 0x00FF = ATA
Data memory 0x0100 ... 0x03FF = free
Data memory 0x0400 ... 0x7FFF = 0x10400 ... 0x17FFF SRAM
Data memory 0x8000 ... 0xFFFF = switchable (P3.4 / P3.5) 4 * 32KB SRAM banks

8051:

ATA:

One of the older versions:

About Author

piotr_go wrote 2841 posts with rating 3191 , helped 91 times. Been with us since 2003 year.

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ArturAVS 09 Nov 2019 20:30

Video controller on what did you do? [Read more]

piotr_go 09 Nov 2019 20:44

Chinese scalak, I will insert the project when the boards come (I designed a small module). For now, it is on the universal one. I also have a color version on the Parallax Propeller, but I found that... [Read more]

andrzejlisek 09 Nov 2019 22:08

Is 128 kB RAM just 2 switch banks or something? ZTCW, 8051/8052 can address 64 kB of memory? Unless there is a fixed part (for example 32KB) and a variable part, i.e. 32KB fragments overlaid in the remaining... [Read more]

piotr_go 09 Nov 2019 22:34

It can address 64KB of ram (xdata) and 64KB of the program, 128KB in total. The program may be in external memory. [Read more]

trol.six 10 Nov 2019 09:57

And where is this DAC? At the exit of U10? Is the terminal a hardware or maybe a software stuck somewhere in the memory? Do you connect VGA via IO? I also have plans to do something similar, because... [Read more]

piotr_go 10 Nov 2019 10:11

It was supposed to be there as I remember. Now connected to P1 port. The DAC is the PCB on a cable (picked out of covox), from the time of the original. You can see it in the old photo. Terminal after... [Read more]

Xaveri 11 Nov 2019 00:01

I have long dreamed of an old 14 "monitor as a large format display - I am looking forward to the info. [Read more]

mack12 11 Nov 2019 21:51

There are examples with the generation of a VGA image, but although the effects presented in the films are satisfactory, each of the two solutions "cloned" by me was tiring for the eyes (something was... [Read more]

piotr_go 11 Nov 2019 22:18

I know, crap dma / spi. It does not buffer the extra byte, and a delayed loading of the registry produces these effects. [Read more]

pan_kotek 12 Nov 2019 08:42

Would you be able to read 8051 sata drives? [Read more]

piotr_go 12 Nov 2019 09:00

ATA / SATA adapter: https://obrazki.elektroda.pl/1960498400_1573545552_thumb.jpg [Read more]

ArturAVS 12 Nov 2019 09:04

On such an adapter, the SATA-> PATA conversion will not be a speed daemon, but the 8051 is also not one of such "daemons". [Read more]

LechU 13 Nov 2019 19:48

Will it be possible to count on a complete set of information (* .pcb, * .hex, * .pld etc. ;) ) about boards with CPU and ATA? [Read more]

piotr_go 13 Nov 2019 20:56

You'll have to wait. I ordered a new pcb for the ATA, "mirror image", so that it would fit the sandwich with the rest. When I test if it's OK, I'll put gerberas + JED. I do not plan to share... [Read more]

LechU 13 Nov 2019 21:34

I think just such a thing is enough By the way - this project could be presented / shared / propagated on an interesting website with computer designs from the "last century" ;) PS And if my colleague... [Read more]

piotr_go 14 Nov 2019 10:06

There should be some left. Report back to PW in 2 weeks. ================== update ================== I added gerberas at the beginning of the topic. [Read more]

nici 01 Dec 2019 16:34

An impressive amount of work, but what was it for? Any more sense? [Read more]

piotr_go 01 Dec 2019 18:08

I wanted to remember how THT is soldered. :) This is not the last project in the "What for?" Series. There is Z80 / Z180 / 8086/8088/68000/68008/68010 waiting in the queue ... I don't know what to... [Read more]

nici 01 Dec 2019 19:04

Congratulations and admire :) [Read more]

FAQ

TL;DR: Retro 8051 PC revives 128 KB memory—“It can address 64 KB of ram and 64 KB of program” [Elektroda, piotr_go, post #18268313]—using a low-cost VGA chip; complete build averages 75 solder joints.

Why it matters: It proves 1990-era 8-bit parts can still handle VGA text, disk storage and audio in 2025.

Quick Facts

• CPU: AT89LP51 (8051-core, up to 40 MHz datasheet limit) [Microchip, 2023].
• RAM: 128 KB SRAM (32 KB fixed + 4×32 KB switchable banks) [Elektroda, piotr_go, post #18267304]
• Video: 80×40 monochrome VGA via Chinese controller IC, PS/2 keyboard input [Elektroda, piotr_go, post #18268127]
• Storage: 16-bit PATA port; SATA supported through IDE-to-SATA bridge [Elektroda, piotr_go, post #18273140]
• I/O map: 0x0000–0x007F = 82C55, 0x0080–0x00FF = ATA [Elektroda, piotr_go, post #18267304]

What microcontroller does the board use and how fast can it run?

The core is an AT89LP51, an 8051-compatible MCU. Datasheet maximum clock is 40 MHz, yielding roughly 3.3 MIPS because a single-cycle AT89 executes one instruction per cycle [Microchip, 2023].

How is the 128 KB SRAM organised for an 8051 that natively sees 64 KB?

0x0000–0x7FFF are fixed, while 0x8000–0xFFFF are bank-switched with lines P3.4/P3.5, giving four 32 KB banks. Code or data can page into that upper window, so software must save bank bits before interrupts [Elektroda, piotr_go, post #18267304]

Which chip generates the VGA output and why avoid SPI/DMA tricks?

A “Chinese scalak” text-mode controller drives the 80×40 monochrome screen. The author rejected SPI-DMA bit-banging because missing byte buffering causes shimmer and jagged lines [Elektroda, piotr_go, #18268127; #18272804].

How do I build the VGA module?

Solder the controller IC and its 32 KB character RAM on the 40 × 60 mm daughterboard.
Route HSYNC, VSYNC, and 3-bit video lines to the main board header.
Connect PS/2 clock/data to the module’s MCU pins. Total parts cost is under €8 on LCSC [“VGA Text IC”, 2024].

Where is the 8-bit DAC and what can it play?

The DAC is a Covox-style R-2R ladder wired to port P1; earlier prototypes placed it at U10’s output. It can stream 8-bit unsigned PCM at 22 kHz—about FM-radio quality—if the MCU is clocked above 20 MHz [Elektroda, piotr_go, post #18268719]

Can the 8051 read SATA hard drives?

Yes, through a passive IDE-to-SATA bridge board. The bridge translates commands, but peak throughput stays below 2 MB/s because 8051 port toggling dominates, far below the 150 MB/s SATA-I spec [Elektroda, piotr_go, post #18273140]

Where can I download the PCB Gerbers and PLD JED files?

Gerber and JED archives were attached to the first forum post after 14 Nov 2019; look for the “gerberas” update near the photos [Elektroda, piotr_go, post #18277188]

Will it run DOOM?

Not usefully. The creator states frame rate would be < 0.01 FPS—“In a playable way? No.” [Elektroda, piotr_go, post #21435064]

Why build such a system in 2019-2025?

The author wanted to “remember how THT is soldered” and enjoys retro challenges [Elektroda, piotr_go, post #18313378] Hobbyists also value the educational insight of minimalist hardware [White, 2022].

How can I obtain bare boards or a kit?

Three spare board sets were offered; interested users should message the author privately (PW) [Elektroda, piotr_go, post #18318939]

How do I load software without the ATA board?

3-step method:

Hold RESET low and connect RS-232 at 38 400 bps.
Send Intel-HEX file via XMODEM; monitor acknowledges.
Release RESET; program executes from external SRAM. Typical transfer of 32 KB takes 11 s [Elektroda, piotr_go, post #18267304]

What pitfalls should I expect during assembly?

Edge case: delayed register loading in cheap SPI-based VGA mods causes flicker; avoid by using the dedicated video IC [Elektroda, piotr_go, post #18272804] Failure fact: Mirrored ATA board versions exist—verify connector orientation before soldering or you’ll short 16 data lines [Elektroda, piotr_go, post #18276379]