You can assemble the sources with the assemblers with one of these fine assemblers:

• TASM Telemark assembler, runs on Windows 10 and 11. My favorite.
• A65 assembler, run in DOSBOX or VDOS.
• ASM.80 online assembler
• the assembler from the CC65 suite, powerfull but perhaps overkill for small programs

Other tools that may help you:

• binary file compare (I use freeware WinMerge)
• hex editor (plugin for Notepad++)
• convert between different 8 bit binary files format such as MOS Papertape, Intel Hex, Motorola S-Record, hex dumps. I use my own tool for that: Convert 8bit hex formats

Note that all these assemblers have a different idea about pseudo ops.

• Some require a ‘.’ in front of a pseudo-op like .org
• db, dw instead of .byte, .word
• > < to indicate upper or lower byte, TASM does not know this, use & $FF and >> 8 to mask of upper byte or move upper byte to lower byte.
• 0X or $ to indicate hexadecimal notation

Easy to edit with a Search and Replace usually.

TASM – Notepad++ integration
Install plugin NPPEXEC

• Place TASM in a folder on your disk, e.g. C:\TASM
• Create environment variable TASMTABS with value C:\TASM
• Add c:\TASM to the PATH

Create a NPPEXEC script:

tasm -65  -g3 -s -l  -c -fff "$(FILE_NAME)" "$(NAME_PART).bin"  "$(NAME_PART).lst"  -s "$(NAME_PART).sym"

(-c to combine parts into binary file, -f to fill unused parts in binary with $FF, see TASM manual)

or to produce Intel hex for a programmer:

tasm -65 -x3 -fff -g0 -c -s "$(FILE_NAME)" "$(NAME_PART).ihex"  "$(NAME_PART).lst"  -s "$(NAME_PART).sym"

(-x3 to allow 65C02 instructions)

Now you can edit a source file, save it (CTRL-S), and press CTRL-F6 to execute the NPPEXEC script. The output of TASM is shown in the windows below the source.
If all is well, a Binary, a listing and a Symbol file is produced.

See also:

Part 4 Sorbus runs Wozmon, Apple 1 Basic, MCP

The first test run of the Sorbus computer can be done with two simple images: Wozmon with Apple 1 Basic and the MCP prog...

Sorbus computer part 3: the hardware

The hardware of the Sorbus computers could not be simpler. Designed with care to be as flexible as possible, fully progr...

Sorbus computer (part 2)

Soldering the PCBs I got from Sven PCBs for the Sorbus and the Sorbus Junior. It took an afternoon to solder all part...

The Sorbus computers

A new development! A minimal 65(C)02 system, called Sorbus designed by Sven Oliver Moll (SvOlli). Thank you Sven for th...

Text on this page and gerbers by Werner Beukes (original site disappeared late 2022)

The Junior Computer was published in the May 1980 issue of the Elektor magazine. Like many single board computers of that time, it was based on the 6502 microprocessor and the design was more or less the same as the Synertek SYM-1 and the KIM-1.

The Junior Computer was part of a bigger system and a year later in the May and June 1981 issues, the interface card was featured. This was followed by the floppy disc interface in the November 1982 issue. What is notable about this design, was that it did not use any of the exotic and hard-to-find floppy disc controllers (and expensive too).

Other cards that were published but not necessarily for use with the Junior Computer only, were the Universal Memory card (March 1983) – and Universal VDU card (September 1983).
The one thing that puts people off from building something like the Junior Computer, is the printed circuit board. It is no longer available through the Elektor’s PCB service and making one yourself from the layout in the article is just too much effort.

Well, I made building your own Junior Computer a lot easier. Using Sprint Layout 6.0, I replicated the designs for the Junior Computer, Interface board, Floppy Disc Controller, Universal Memory card and Bus board.
The Gerber files for these boards are available free for download and the printed circuit boards made from these files will result in boards which would be identical to the ones you would have received should you have ordered it from the PCB Service..

Downloads here:

• Original Junior Computer
  This download includes all the Gerber files, the layout file
• Modified Junior Computer
  There are 2 modifications. The crystal replaced by 1MHz crystal oscillator and 2708 EPROM replaced by 2716 or 28C16 EEPROM.
• Interface Card
  Project published Elektor May 1981 and June 1981. This was extremely difficult to replicate as the artwork quality was very bad.
• Floppy Interface Card
  Project published in Elektor November 1982. Design does not use exotic (and hard to find) floppy controllers like the WD1770 etc.
• Universal Memory Card
  Article published in the Elektor of March 1983.
• Bus Board
  Required if you want to put a full system together.
• Mini Bus Board
  Couple Junior and Interface card.
• VDU card with BNC

Junior Computer ][

Written by 2021 by Joerg Walke, visit his webiste for the most actual version!
The Junior Computer ][ is an expanded version of the original Junior Computer. To make it more useful, I’ve equipped it with 32KB RAM, 8KB ROM and an onboard RS232 serial interface for connecting a terminal or a printer. For the use with a terminal, I also wrote an extended monitor program thats included in the bigger ROM. The development of the Junior Computer ][ is still in progress, so some other features will find its way to the mainboard.

On the picture above, you can see the actual rev. 2 board of the Junior Computer ][.
The new revision 3 board has arrived!

…all components assembled and soldered

…and it works fine!
Its new features are: Up to 128KB RAM chips installable. 3 DIP switches to configure three additional 8KB RAM banks. Maximum of 51712 Bytes usable with 64KB RAM chip. Auto reset at power on. A power switch (oh yeah). Usable Memory for string buffers in the address area of the ACIA.

Edit August 2022: there is now also a I/O card and a bus card!

The Computer is divided into two parts. On the left side are the main computer components. The 6502 CPU, 6532 RIOT (RAM, Input/Output and Timer), ROM (8 KB EPROM), RAM (32 KB SRAM), the 1MHz quarz cristal and some 74LSxx logic chips for address decoding and clock generation. There is also a double timer chip on the lower left corner for debouncing the Reset (R) and Stop (S) keys. On the top lies the (in the picture not populated) expansions connector. And on the bottom side there is a connector for the two 8 Bit I/O ports coming from the 6532 RIOT. A small transistor amplifier on port B0 can be used to drive a loudspeaker, to make some simple noise.
The input/output components of the Junior are on the right side of the PCB. There is the hexadecimal keyboard, for entering the program addresses and data. And there are also some control keys. Above the keyboard is the six-digit, 7-segment display for showing the addresses and the data bytes as hexadecimal coded numbers. The display can also be switched off, if not needed. Keyboard and display is controlled by the two 8-bit I/O ports of the RIOT, by alternately polling the keyboard and repeatedly writing each single digit of the data to be shown on the display. On the top of the I/O side is the 6551 ACIA (Asynchronous Communications Interface Adapter) chip and a level shifter for the RS232 serial interface signals. The little quarts aside the ACIA is for the baud rate generation, which ranges from 50 to 19200 Baud.
I built the first prototype in July 2020 on a breadboard, followed by the rev. 1 PCB in August 2021.

The rev. 2 board was necessary, because unfortunately the distances between the input keys were a little bit too narrow. Also the rev. 2 board had some issues. But it worked fine for me. After publishing the JC][ on the Classic Computing forum (www.classic-computing.de), I found some people who were interested in it. That charged me to make some further expansions and to make it a little bit more useful for others. The revision 3 board with some improvements is now on the way, as is new software.
The schematics and Gerber files for the PCB and of course the ROM images and the 6502 Assembler source code files are freely available on the download section. So feel free, to make your own Junior ][ and have some fun with 8 bits.

Programming the Junior Computer ][

Programming the Junior is quite simple:
Apply power and press the (R)eset switch. The display turns on and shows a random memory address (four digits) and its content (two digits). The Junior Computer ][ and its predecessor are both programmed in raw 6502 machine language. That is, each CPU command is entered in its numeric representation as a hexadecimal number. For example, 4c 00 F8 means: Jump (4C) to absolute location F800. 16-bit values such as memory addresses are written as the lowest byte first, so the byte representation 34 12 in memory represents the 16-bit value 1234 in hexadecimal.
To enter some data, you first have to type the address, were the data should be located. To do so, press the (AD)dress key and type in the four hexadecimal digits (16 bits) of the memory address location. Then press the (DA)ta key and type the two hexadecimal digits (8 bits) of the data. If you make a mistake, simply type in the new value. To enter data in the immediately following address, press the + Key (in my picture above, this is the down arrow key – because I just hadn’t a + keycap) and enter the new data.
To examine any address, you just have to press the (AD)dress key again and type in the address you want to visit. By pressing the + key, the direct successor address is displayed. Pressing the GO key executes the program at the currently displayed memory address. There is also a Edit mode where you can insert and delete data, and automatically calculate branch and jump addresses. To use this mode, please refer to the Junior Computer Book 2.
Another way to enter programs is, to use the extended (terminal) print monitor program. First you have to connect a VT100 compatible terminal to the RS232 interface and set it to

9600 Baud, 8 data bits, no parity, 1 stop bit

To start the monitor program, press the (AD)dress key, type in the address F800 and press GO. On the terminal display, you should now see something like this:

                                  Junior Computer ][

Print Monitor
2021 by Joerg Walke

(M)onitor  (L)oad  (S)ave  (A)ssembler  (B)asic ?

For now Monitor is the only selectable choice (but the rest will come soon, hopefully), so type M on the terminal keyboard to enter the Hex Monitor. The Display is cleared and a * prompt is shown. All input is non case sensitive, so typeing M or m is the same.
To examine the content of a single address, just type in the address as a hexadecimal number and press the Return key. The address and its current content is then shown.

*F800

F800- 4C

To view a hole block of data, enter the start-address and the end-address of the block to be shown, divided by a . (dot).

*F800.F808

F800- 4C DC F8 A4 F8 B1 F6 E6 
F808- F8

To enter new data, type in the address where the data should be written, followed by a : (colon), followed by the single data bytes.

*200: 4C 00 F8

0200- 03

Execute a program by typing the start address followed by a G

*0200G

0200- 4C

To exit the Monitor and to go back to the main screen of the monitor type

*X

and then press the Return key.
If you want to go back to the standard Junior Monitor just enter

*1C1DG

(followed by Return) which leaves the terminal screen as a Zombie without a function and enables the 7-segment display and the hex keyboard.
That’s it. If you are interested in learning more about programming the 6502 and the Junior Computer, please refer to the MOS 6502 Datasheet and the Junior Computer books.

Downloads Junior Computer ][

Downloads Junior Computer ][