Tag Archives: old-computers

Assembly in Dosbox, and draw a line

Below my setup in Dosbox.
(As used 30 years ago)

First install dosbox (Linux/Windows)

download the package with used files and compilers from here:

extract with tar xzvf /tmp/assembly.tgz to a directory

start dosbox and mount the directory as C

mount c /path/assembly

Run “a line”, this a batchfile which starts the editor (qedit)
When closing the file (esc – q menu)
It will compile the assembly and write out a executable

This is the batchfile

@echo off
q %1.asm
masm %1.asm;
link %1.obj;
exe2bin %1.exe %1.com
echo READY!

line assembly code

    NAME lijnentrekroutine


    ASSUME CS:Code,DS:Code
org 100h
    mov ax,13h            ;set video mode
    int 10h

    mov bx,100
    mov cx,100
    mov dx,0a000h
    mov es,dx
    mov ax,320
    mul cx
    add ax,bx
    mov di,ax
    mov al,2
    inc bx
    inc bx
    inc cx
    cmp bx,150
    jnz hiero

    mov ah,8
    int 21h
    mov ax,3
    int 10h

    MOV AX,4C00h
    INT 21h

code ends
end start

Hercules to VGA

While playing with MuseScore….
(Typesetting some scores for Pipes and Flute)

This came in: WOOOT

Trident 8900C (1024 x768 max 512Kb)

This is a Trident VGA card. While having a 16bit ISA connector, it can work in a 8bits ISA slot.

A while ago i bought a Laser XT/3, that’s the one my parents had.
This is where i did a lot of assembly programming on.
It’s a 8086 cpu, 640K and has a Hercules/CGA graphics card.

I found loads of assembly files and i want to see if i can get it running again.
While some code was written for hercules, ( That’s the monochrome image you see in the example above ) and a few for EGA (4 colors).

Most of it was written for VGA. Probably on a later machine like a 80386?

But i know there are vga cards for 8 bit msdos computers, and i found one. ( This one is even autodetect, so no jumpers to figure out)

So i’ve put this card in the machine, turned it on, and it works!
I’ve got only 2 examples living on the harddisk of the machine, both black and white … 🙂
I have to search for interesting code in hundreds of files.

Some friends of mine, picture was taken from an amiga genlock digitizer
The intro pages of a “amiga emulator” WHERE is the rest??? (end is a cga starfield demo)

Hercules Card

There is not much info available about this card:

  • Max resolution (Hercules) : 720×348
  • 15 pin analog monitor port (CN1)
  • BIOS enabled JP1 Pins 1 & 2 closed
  • BIOS disabled JP1 Pins 2 & 3 closed
  • CGA selected SW1 On
  • MDA (Hercules) selected SW1 Off

Floppy drive boot

My friend EDK and I made some demo’s like

And a boot demo, which was able to start from a bootsector, went into a graphic mode and ran a demo with sound. Edk wrote a sector loader for this.
I have some 5.25 inch floppy disks, labelled boot demo. So i wanted to try this today …
I needed to change the boot order, so i went online to search for jumper settings.

I see a led when it tries to boot, but my disks are probably formatted 720Kb instead of 360Kb, which this drive is.

So …. TODO!

Find a 720Kb floppy drive (5.25 inch), and sort through my code!
There is a 8bit soundblaster compatible soundcard that i bidding on online, hopefully i’ll get it

Assembly and modes

I wasn’t sure how to sort the assembly code into Hercules and VGA compatible, but i used this table (There are also extended modes for higher resolutions)

mode 0x00text 40×25 gray
mode 0x01text 40×25 16 colors
mode 0x02text 80×25
mode 0x03text 80×25 16 color
mode 0x04graphics mode (CGA) 320×200
mode 0x05graphics mode (CGA) 320×200
mode 0x06graphics mode (CGA) 640×200 (B/W)
mode 0x07text 80×25 Hercules
mode 0x0Fgraphics mode 640×350? gray
mode 0x10graphics mode 640×350?
mode 0x11graphics vga 2 colors
mode 0x12graphics vga 16 colors
mode 0x13graphics 320×200 256 colors
# Set VGA mode
    mov ax,13h
    int 10h         ;screen 320x200 256 colours

# Exit VGA mode
    mov ax,3
    int 10h         ;screen  80x25 text
    mov ax,4c00h
    int 21h         ;back to DOS

7 segment displays/keyboard decoders in SDK’s

There are a lot of old develop boards for all kinds for cpu’s.

These where build to learn machine code programming. Mostly made in the 80’s, and based on populair cpu’s at that time.

I own a some of these SDK’s (Software development Kits)

8085 – SDK85 i bought recently 8085 CPU
Microprofessor-1 (MPF-1) Z80 CPU
And my own 680x based computer

Most of these use a keyboard scanner which is also connected to 7 segment displays.

The way they work is practically the same. There is a VIA or PIA. Versitile interface adaptor, or Peripheral interface adaptor. These have two times 8 bits to control devices.
When using 4 bits and convert these to 16 lines by using a 75ls145 for example. If you put a counter on those 4 bits, you sequently activate 1 of 16 lines. These lines you can use to scan a keyboard matrix OR display a character on a 7 segment display. These display’s won’t hold the data (and show the character) when not activated. The trick is to update de display fast enough so you don’t see the flickering on/off.

Activate a line and read a byte with the VIA = Reading keyboard row
Activate a line and write a byte with the VIA = Display on a segment

These VIA/PIA’s where made with specific timings to match the CPU.

Below you see some different implementations of these keyboard/display combo’s

Thaler 6502 kit
Microprofessor MPF-1 kit (ignore red circle)
SDK85 kit
Eltec 6800
My version using darlington arrays (ULN2003)

When looking at the 8085 version you see transistors being a ULN2003 is a chip with those transistors/amplification enclosed.
It doesn´t draw much current from the bus, and diodes protect the way the current flows.

SDK-85 searching archives

Found these old .. old mini-cassettes .. wish i could read these now.
The sdk units we had, had tapedrives and few other hardware devices you could play with. Like a motor you could control, which had a disc with slots in it on top. These slots could be read and counted with a sensor to determine the speed.

Also this scanned pages, from school i found. There should also be a little notbook with programs and notes ..

Found some ROM files also

Apparently we had something called a bb-board.
These had motors and speakers and such

This part contains the motor with sensor
Led and switches
Speaker and more

I want to try to get some parts working by rebuilding. Like the speaker .. because … i found some own written software!

I found als programs written by my friend Martin

SDK-85 in 2022

I was posting about the 8085 software development kit in may, but now i’ve got one!

I found one online, it is a very clean almost like its never been used version!

More follows!

More info at http://www.bitsavers.org/components/intel/8085/

Selling a lot of my computer collection

The last days i’ve been selling a lot of my old computers.
They have been in my collection for many years, but now its time to part.
Time for others to enjoy them.

(Instead of posting which ones are being sold and which i’ve still got on this page i’ll make another post)

I started collecting when i studied computer sciences.
It’s a wonder my parents attic wasn’t collapsing.
(They let me store many computers on their attic, let me run a mainframe in the house (previous post) and let me have computer-parties (pre-lan) in their home. (They even left, and gave me the space) .. 15+ teens with computers … there was a pingpong table in the livingroom (besides the other tables in the house ) For all computers.

Then i’ve got even more, when living on my own. (At some point about 140. )

A few years later i got rid of uninteresting computers (to my taste at that time) and incomplete ones. Then i filtered-out the non working.

Still leaving with a lot of computers, i kept these for many years.

Now i only want the ones i’ve worked with, or are special to me.

My first computer was a Commodore Vic-20. Friends had the popular C64. So i kept 2 of both.
In Junior Technical School i’ve used the BBC Acorn a lot (Funny story below)
My then friend Richard had a Atari ST, loads of fun we had with that machine, so i’m keeping a Atari 1040STf.
Another friend used a Apple SE, so that one i also keep for now.
I’ve been programming a lot on 80×86, the first dos PC’s, i’m still looking for a old machine (Laser XT) which i used way back then. But for now i’ve got a Sinclair PC200.
I’ll keep a old Commodore PET 2001, because its cute.
Besides having a cute PET, i’ve got a Holborn System. Made in Holland (Enschede), there are only a few left according to some sites: only 200 made! (Holborn means Holland Born) One of the inventors was from Holten, my birthplace. (Polak)

Putting the system together in 2018

At school we kept a list of everyone’s collection.

Soo .. the story about the BBC Acorn.

When i was at school outside study hours, i went to the computer lab.
This was one classroom with about 16 BBC Acorns and a master (teacher station). When they saw how enthusiastic i was, i got the key to the classroom. I even got access to the master system. And after a little hacking i’ve gained access to the teachers files.
There was a simple network system, i think it was called Econet.
The teachers system was the only one with a disk station.

I liked the ‘highres’ line graphics you could make on the machines. (640×256)
So i’ve wrote a lot of programs using this mode.
I even wrote a program which drew a 3D robotarm on screen using wireframe graphics.
At that time my mathematics scores where .. bad.
Wasn’t interested i think.
But drawing 3D robotic arms are not possible using mathematics, like using sinus, triangulary etcetera.
So when my mathematics teacher saw my program, he didn’t believe me.
So .. fooling around in the computer lab, i missed start of classes. And later on .. worse .. i almost was not allowed to do my final exams.
I was late several times (and one of the first to leave, …. straight from and to the computer lab. )

I’ve got some programs printed on paper, i will use my leftover BBC Acorn (or a emulator) to capture some screen examples.

6502 cont.

UPDATE: 20220823 Sid working

Kicad VIA/PIA tester

Above is my Kicad design (reverse engineering print below, which was made for my 6802CPU, which i could use to test the 6822 PIA)
The 6822 is simular to 6502 in design. So i’m going to redo this for my 6502.
The 7 segment displays are a start of hex-keyboard/display combo i’m going to post more of in the next days.

Below a part of the rom for the LCD dual line display.

Part of the ROM assembly code, top part is text (o.a. japanese)

Started to write routines which i can call to manipulate the display. Setting the pointer to a message, setting the line to use and a subset of controlls like: Center, Right, binary to ascii, scrolling, etcetera

        lda #0             ; set line number
        sta lineno         ; store
        jsr gotoline       ; goto line in display
        lda #<message      ; get address from message and store for printline subroutine
        sta messagestore
        lda #>message
        sta messagestore+1
        jsr printline      ; print

        lda #1  ; set line number
        sta lineno      ; store
        jsr gotoline
        lda #<message2
        sta messagestore
        lda #>message2
        sta messagestore+1
        jsr printline

Above additions:
New address decoder
Below left the new graphical display, below right a test board which shows address lines and decoded chip-enable lines.

A15 high -> ROM
A15 && A14 low -> RAM
combination of A15 low and A14 high – A13 and A12 wil select peripherals.

Adress decoding

Above is a start of a wirewrapped version, i also started a PCB design in KIcad that will continuously be changed as i alter designs.

UPDATE SID Working! Using new address decoder.

SID = $7000

	lda #0
	sta SID+$5 ; Channel1 - attack/decay
	lda #250
	sta SID+$6 ; Channel1 - Sustain/Release
	lda #$95
	sta SID+$0 ; Channel1 - Frequency low-byte
	lda #$44
	sta SID+$1 ; Channel1 - Frequency high-byte

	lda #%00100001
	sta SID+$4 ; SAW + Gate

	lda #$0f
	sta SID+$18 ; Volume max

C64 Cartridge

Got IC Sockets in today, together with other goodies.

So i soldered the C64 Cartridge print.

Putting a bin on the eeprom

sudo minipro -p AT28C64 -w 8kcart.bin

Welll .. allmost working.
Some strange artifacts, but is running.

The long wire … is a ‘jumper’ .. i cant find ONE (free) jumper in my lab!

6502 progress

UPDATE: 20220815, 20220814, 20220815

Flashing ROMs .. (eeproms). It used to be a pain in the *$$.
Burning took a looong time. But clearing one with UV took .. 20 minutes or so. Using one of these:

Altered clock module

  • Changed button press
  • Dipswitches for more speed control (red .. upper left)

Changed Rom/Ram

  • Changed addressing
  • Added RAM
  • ZIF Socket for ROM

VIC 6522

  • Fixed clock
  • Added buttons for interrupt


  • Display works now
  • To test: Create Address logic to access display without VIA
    Can work, but not at high speed clock. Stays behind VIA
  • To buy: st7920 lcd 128×64

Generic improvements

  • Rewired most parts, using color codes
    (Blue data, Yellow Address and so on)
  • Added leds on data and address bus using ULN2803 darlington arrays
  • 100nF Decoupling capacitors on the power rails

To do’s or ‘have to look into’s’

  • For sound i planned to use a General Instrument AY-3-8910, it is somewhere in my Lab, i know it is.
    I saved this chip and a SID for my Amiga addon soundcard.
    Where are my plans for the simple v1 setup?
  • I have to start writing rom functions for display usage. Like
    JSR $ff00 – Clear screen subroutine .. etc
  • I’m scraping information from websites, to get started on my clock controller.
    ATmega328 with ssd1306 display and rotary encoder/dip switches

Notes about the movie:
Left side is Arduino IDE monitor reading Addressbus and Databus.
(I’m going to try to rewrite this to realtime disassemble)
Resetting system.
Stepping CPU with manual clock pulses.
Start vector being read at $FFFC/$FFFD.
Program being run from $8000.
Set clock on automatic ( ~ about 150 Hz )
Last opcodes you see a JMP loop 4C 2F 80, that is JMP $802F
Display enlarged on video, was not visible on movie i took on mobile.
(Wrong angle?)

Breadboard overview

Clock moduleReset module + Crystal
CPU + nmi/int buttonsRAM and ROM
Address decode + Bus divideAddres/Data bus leds
6522 VIA + Display2nd via + Buttons
?(sound board)

TIL: 6502 can run without ram only rom,expect when using JSR … which uses a program stack in RAM


  • Make Clock module and 1Mhz Crystal switchable
  • NMI and INT debounce maken
  • Software buttons
  • Buy new darlingtons, for controlbus!
    • r/w, int, chip enables, etc
  • Labels on chips/breadboards

C64 PRG to cartridge.

I’ve got the tools and Bigred made me enthusiastic again.
My goal is to make a C64 Cartridge from a PRG. And Not any program, it is the 8085 Emulator from Sepp.

Serveral problems i have to ‘fix’

  • The program is 17K, Cartridges can only be 16K.
    So i have to use 2x 8K and compress the data.
    This means it have to be uncompressed at start time.
    ( I was thinking of using exomiser for this )
  • Program starts normally at $0820 and probably is not optimised to run anywhere else.
    So a starting routine has to copy the program from cartridge memory to the correct location

Luckily i have the source! How cool is that

For version 4.73 it states : Starting at $0820 .. but my hexdump is off by one??!?

root@battlestation:/home/fash/Projects/minipro# hexdump -C /tmp/8085.prg  | head
00000000  01 08 1e 08 c5 07 9e 32  30 38 30 20 42 59 20 4d  |.......2080 BY M|
00000010  41 52 54 49 4e 20 4d 45  59 45 52 49 4e 4b 00 00  |ARTIN MEYERINK..|
00000020  00 20 ec 08 20 7f 19 20  2b 2c 20 11 19 20 b8 08  |. .. .. +, .. ..|
00000030  20 20 2c 20 a0 2c 20 f2  2c 20 11 e1 4c 00 15 aa  |  , ., ., ..L...|
00000040  aa a2 06 ad b7 08 9d 48  d8 bd 48 04 20 88 39 9d  |.......H..H. .9.|
00000050  48 04 ca 10 ee a9 60 8d  4c 04 4c 50 47 00 a9 d0  |H.....`.L.LPG...|
00000060  2c a9 f0 8d 45 1f 4c 11  e1 1e 93 0d 20 20 4d 41  |,...E.L.....  MA|
00000070  52 54 49 4e 20 4d 45 59  45 52 49 4e 4b 27 53 0d  |RTIN MEYERINK'S.|
00000080  0d 20 38 30 38 35 20 45  4d 55 4c 41 54 4f 52 20  |. 8085 EMULATOR |
00000090  20 56 34 2e 38 30 0d 0d  20 20 28 43 29 20 31 20  | V4.80..  (C) 1 |

00000020 00 20 ec starts with 00 at $0020 .. and not 20 ?!?!

Tools used until now:

  • Vice – C64 Emulator
    x64 -cartcrt 8085.crt
  • c1541 – Linux disk tool for C64 images.
    Used this to extract the 8085emulator PRG
  • prg2crt.py – a convertor from PRG to a cartrid file which can be used by Vice
    python2 prg2crt.py 8085.prg 8085.crt
  • minipro – eeprom programming tool for Linux
    minipro -p AT28C64 -w /tmp/test.bin
  • cartconv (tool from vice to convert crt <-> bin)
    cartconv -t normal -i test.bin -n ‘my cart’ -o test.crt
  • xa – Cross assembler 65xx/R65C02/65816
  • ACME – the ACME Crossassembler for Multiple Environments
Memory Map C64 – source c64-wiki.com

Card Low starts at $8000, so that’s the place where those roms are going to be.
To place on this address:

Copy routine : from ($8000 + this copy routine) to $0820
When to decompress??
jmp routine to $0820

A cartridge file >16K and with his emulation headers seems to work??!

Also nice: Magic Desk Cartridge Generator V3.0

UPDATE: 20220811

exomizer sfx 0x0820 8085.prg -o data.exo # Compress and start at 0x0820 
xa frame.asm -o frame.bin # Add code and write binary
x64 --cart16 frame.bin # Test cartridge with Vice


; example usage
; xa frame.asm -o frame.bin
; cartconv -t normal -i frame.bin -n 'my cart' -o frame.crt
; x64 -cartcrt frame.crt

;no load-adress for bin-file, so no header here

.word launcher ;cold start
.word launcher ;warm start
.byte $c3	;c
.byte $c2	;b
.byte $cd	;m
.byte $38	;8
.byte $30	;0

  stx $d016
  jsr $fda3	;prepare irq
  jsr $fd50	;init memory
  jsr $fd15	;init i/o
  jsr $ff5b	;init video
                ;make sure this sets up everything you need,
                ;the calls above are probably sufficient
  ldx #$fb

;set up starting code outside of cartridge-area
  ldx #(starter_end-starter_start)
  lda starter_start,x
  sta $100,x
  bpl loop1
  jmp $100
  ldx #$40 ;64 pages = 256 * 64 = 16384 Bytes
  ldy #0
  lda exomized_data,y
  sta $801,y
  bne loop
  inc src+2-starter_start+$100 
  inc dst+2-starter_start+$100
  bpl loop

;make sure settings for $01 and IRQ etc are correct for your code
;remember THIS table from AAY64:

;       Bit+-------------+-----------+------------+
;       210| $8000-$BFFF |$D000-$DFFF|$E000-$FFFF |
;  +---+---+-------------+-----------+------------+
;  | 7 |111| Cart.+Basic |    I/O    | Kernal ROM |
;  +---+---+-------------+-----------+------------+
;  | 6 |110|     RAM     |    I/O    | Kernal ROM |
;  +---+---+-------------+-----------+------------+
;  | 5 |101|     RAM     |    I/O    |    RAM     |
;  +---+---+-------------+-----------+------------+
;  | 4 |100|     RAM     |    RAM    |    RAM     |
;  +---+---+-------------+-----------+------------+
;  | 3 |011| Cart.+Basic | Char. ROM | Kernal ROM |
;  +---+---+-------------+-----------+------------+
;  | 2 |010|     RAM     | Char. ROM | Kernal ROM |
;  +---+---+-------------+-----------+------------+
;  | 1 |001|     RAM     | Char. ROM |    RAM     |
;  +---+---+-------------+-----------+------------+
;  | 0 |000|     RAM     |    RAM    |    RAM     |
;  +---+---+-------------+-----------+------------+

  lda #$35 ;cart is always on instead of BASIC unless it can be switched off via software
  sta $01
  jmp $80d ;for exomizer, i.e.

.bin 2,0,"data.exo"
;syntax for exomizer 2.0.1:
;exomizer sfx sys game.prg -o data.exo
;fill up full $4000 bytes for bin file ($c000-$8000=$4000)
.dsb ($c000-main_file_end),0

Exomiser info

 Reading "8085.prg", loading from $0801 to $4CE9.
 Crunching from $0801 to $4CE9.
Phase 1: Instrumenting file
 Length of indata: 17640 bytes.
 Instrumenting file, done.

Phase 2: Calculating encoding
 pass 1: optimizing ..
  size 80273.0 bits ~10035 bytes
 pass 2: optimizing ..
  size 80039.0 bits ~10005 bytes
 pass 3: optimizing ..
 Calculating encoding, done.

Phase 3: Generating output file
 Encoding: 1101112133423160,1122,2010223445667788,032144406789BBCD
 Length of crunched data: 10034 bytes.
 Crunched data reduced 7606 bytes (43.12%)
 Target is self-decrunching C64 executable,
 jmp address $0820.
 Writing "data.exo" as prg, saving from $0801 to $304C.
Memory layout:   |Start |End   |
 Crunched data   | $07E7| $2F18|
 Decrunched data | $0801| $4CE9|
 Decrunch table  | $0334| $03D0|
 Decruncher      | $00FD| $01C0| and $9F,$A7,$AE,$AF
 Decrunch effect writes to $DBE7.
Decruncher:  |Enter |During|Exit  |
 RAM config  |   $37|   $37|   $37|
 IRQ enabled |     1|     1|     1|