VDU card for Junior with OS65D

Philippe Roehr has remade a VDU PCB as featured in the Elektor Junior articles and put it to work with his OS65D system.



In the Elektor Specials Elektor bus based systems were presented that could be used to build more advanced computers, based on the 6502, Z80 of 65816.

Several names were used for systems, like EC65 and Octopus and you see in these pages many references to these cards, like DOS65, Elektor articles and books

See below for the Elektor Specials with EC65 etc articles.

See also the Z80 Elektuur/Elektor pages

Download here the EC 65 Octopus ROMs, dumped from CPU cards

Elektor bus

From Martin Seine I have received the source of the EC65 ROM and the system disk of the EC65 system

Disassembled, sorted and and somehow aligned the original SAMSON EPROM. The assembler file is here. It will compile byte identical with ca65. All upper case labels match the documentation I have found. The lower case labels are made up by Martin, because they are needed in there. There is a disassembler in the monitor rom, which I did not analyze and hence the disassembly is just strong bytes in that section.

Martin has recovered some original EC65 disks. Here the original disk#5, which is the „System Disk Loys“ as HFE image, which will run on EC65 with Gotek FlashFloppy. Amrtin has now a running EC65 with original system disk. The HFE is the 80-track version and a double side image, but it works as one side as well.

Elektuur Computing 1
Dutch, Octopus/Samson 6502 computer
Sonderheft German
Elektuur Computing 2
Dutch, More 6502 computer
Elektuur Computing 3
Dutch, More 6502 computer
Elektuur Computing 4
Dutch, EC65K and more

Elektuur Computing 5
Dutch, Z80 and more 6502 hardware and software
Elektor Computing 5 German

Adding I/O to the KIM-1

By Bob Applegate

Adding I/O devices that don’t need much address space. On the KIM-1, the space from 1400-17FF is grouped into the K0 block but only 17xx are used, leaving 1400-16FF open for use. To decode that range into four blocks of 256 bytes is easy using a single chip and a few signals from the KIM Clone expansion bus:

Everyone has a 74LS138 in their parts collection, so just connect a few signals from the expansion bus and use one of the three signals from the 138 to decode which block you want to use. Use the A0-A7 address lines to decode into smaller pieces.


Using KIM Clone I/O

By Bob Applegate

KIM Clone I/O Not Receiving Serial Data

While testing the KIM Clone I/O Board I was using a real ASCII terminal and everything was working exactly as it should. After the board was in product a dedicated tool was written to run complete tests of the board and the serial port was no longer receiving data.

As it turns out, it is possible to set the various jumpers on the board so that the DCD line on the 6850 is floating, and it tends to float to a state where it ignores incoming data. My test jig simply loops back pins 2 and 3, leaving DCD unconnected.

The easiest solution is to pull the jumper off JP8, then place it between pins 6 and 7 on JP10. This forces the DCD to ground, which allows the receiver to work as expected.

Depending on your application, whatever is connected to the DB-9 might pull DCD to the active state which also allows the receiver to work properly.

Future revisions of the board will have a pull-down resistor on both DCD and CTS so unconnected inputs will default to the proper levels for normal operation of the ACIA.

Using I/O lines

Like the original KIM-1, there are 16 I/O lines on the KIM Clone that can be used for your own projects. They are brought to the connector labeled “SD SYSTEM” along the top edge of the board and were meant to plug into one of our SD Card Systems for program storage. However, they are general purpose I/O lines which can be freely used for other things if the SD system is not used.

This is a portion of the schematic showing which pins on the 6532 are connected to which pins on the connector:

Don’t worry about the signal names associated with the various lines, they are the names of those signals when an SD Card System is attached.

As you can see, there are 16 IO lines, 2 ground lines, and 2 lines with +7.5… if you want to draw power from this connector for TTL/CMOS circuits then you need to add your own +5 volt regulator! D2 prevents back-feeding power from the connector back into the KIM Clone.

On the circuit board, pins 1 and 2 are labeled but are covered by the connector, so here is a reference:

All of the odd numbered pins are on the “bottom” row while even numbered pins are on the top. Ie, the top row has pins 2, 4, 6, etc, while the bottom row has 1, 3, 5, etc. Displaying the circuit board traces on the bottom layer of the board you can clearly see the ground and power lines connected to the pins on the far right:

The datasheet for the 6532 RIOT chip is readily available here.

To program the chip you basically need to set the direction of each pin of the I/O port of interest (Port A or Port B), then set the data or read the data. The base address of the chip is 1700 (hex). There are four registers:

Address Use
1700 Data register A
1701 Data direction register A. Setting a bit to 1 makes it an output bit, 0 makes it an input.
1702 Data register B
1703 Data direction register B. Setting a bit to 1 makes it an output bit, 0 makes it an input.

An Example
I needed to test experimental address decoder logic and found it was easier to just plug it into the I/O ports and write some code on the KIM Clone to simulate the addresses and display what the decoder logic did:

Port A simulates address lines A11-A16 and port B has the three decoder outputs (/RAM, /IO, /EEPROM). A small program simulates all possible values of the five address bits, displays the address, reads the decoder inputs and then displays which are active. In about an hour I was able to fix one minor bug in the decoder design and perform a full unit test on how it works. Certainly not a fancy example of using I/O ports, but sometimes it far faster to build a small circuit and use software to test it rather than building a lot of hardware and manually debugging it all.


New KIM replica PAL-1, Corsham pages enhanced

PAL-1 A new KIM replica, in fact a clone of the Micro-KIM with improvements.

Corsham KIM Clone pages enhanced. At first sight the Corsham pages looked fine, But when I tried to find things I quickly got lost between Product Descriptions, TechTips, Documentation and the Corsham Github page. Old and new, curuent and obsolte, a bit of a mess.
Also most documents are in Word format and I prefer PDF format for reading on my tablet PC’s.
So the Corsham pages are now enhanced for all hardware products I have acquired.


A new KIM-1 clone kit in 2021, the PAL-1. In fact, this is a Micro-KIM clone, which is a KIM-1 clone .. Look and specs are like the Micro-KIM, with some improvements like larger keys and a very affordable price. Motherboard, 32K RAM, second 6532 board, RAM board, ROm board, Cassette board, a full KIM-1 and more compatible system.

Designer and seller is software engineer, Liu Ganning, KJXZZ, from Shenzhen, Guangdong, China

The PAL-1 has its own discussion platform at google groups.
For software: se the KIM-1 software page, as the PAL-1 is a KIM-1 with lots of memory!
PAL-1’s difference
First, PAL-1 is a kit, you can assemble it, test it and run it all by yourself —— an unique experience!
The PAL-1 addressing mode is completely implemented in accordance with the design of KIM-1, so it is compatible with most programs developed on KIM-1.
PAL-1 has 2K bytes ROM (complete KIM-1 Monitor), 5K bytes RAM, one 6532 RIOT chip on board, provides two 8-bit bidirectional I/Os, these I/Os are mainly used to support 23-key keyboard input and drive 6 seven-segment LED displays. In addition, PAL-1 also provides RS232 serial port to support terminal operation and 40-pin expansion port for future upgrade. The TTY/RS232 interface and expansion interface pinout uses the design of Rich Dreher and Vince Briel (MicroKIM compatible).
Besides the PAL-1 also a 6 slot motherboard, a 32K RAM board and a RIOT board (the second 6532 making it a complete KIM-1) and a cassette interface baord are available. A ROM boards adds many programs like programming languages Basic, Forth etc.

The main differences between PAL-1 and KIM-1 are illustrated by the following two figures in the “KIM-1 User Manual”.
PAL-1 absence half I/O and Timer (red) Picture 11 (see the RIOT board how to add this!)

PAL-1 onboard RAM increased to 5K (all green spaces are available) Picture 10

What is included
The PAL-1 Kit includes mainboard PCB, ICs, pre-programmed ROM, passive components, sockets & headers.
Print version BOM, Pinout, Schematic.


User Manual PAL-1
Schematic PAL-1
Bill of Materials
32K RAM expansion manual
32k RAM board schematic
RIOT expansion manual
RIOT board schematic
ROM expansion manual 1.0
ROM expansion manual_v1.2 (28C256)
Operation guide PAL-1 EPROM Expansion Card
ROM board 1.0 schematic
ROM board schematic V1.2
ROM PAL-1 ROM image
Cassette expansion manual
Cassette board schematic
Cassette board BOM

Modification for TTL USB interface

The two following images show how to adapt the PAL-1 to a TTL USB interface instead of RS232. also supplying power from USB.

Modification of ROM board 1.0 for 28C256 EEPROM

The ROM card v1.0 is designed for using 27C256 and 27C512 EPROM, but these UV-erase chip will need much patient when you’re doing a lot of ROM program. So the PAL-1 got a new version ROM card, v1.2, to support the more convenience EEPROM, the 28C256.

Even the v1.0 ROM card designed for the 27Cxxx, you can also use the 28C256 on it. Just one soldering work need to do, populate the high 32K switch using a switch (like K3-2235D-F1) or 3-pin 2.54mm pin header (solder at the inner side of the high 32K switch).

When you need to using a 28C256, you can set and keep the low 32K switch to HIGH, then using the high 32K switch/jumper to select the low 16K bank or the high 16K bank of 28C256 just like normal.

A second RAM board can be modified to add 16K extra.
Modify a 32K RAM card for the upper RAM area. Just need to cut 1 wire and solder 2 jumper wires like below:

The KIM ROM needs the highest area of 64K for the vectors, so the Exxx to FFFF cannot be decoded with the second 32K RAM card.
We can use $A000~$DFFF (16K) more RAM with the second RAM card installed.

Some pictures of the two RAM card system running.

RAM test:

KIM Clone software


Look at the KIM-1 software page for a wide offer of KIM-1 software, suitable also for the KIM Clone.

KIM Monitor

The Corsham variant of the KIM Monitor is for the most part made up of the code in the 6530-002 ROM. The 6530-003 (audio cassette save/load) ROM was removed.
Placed in the main ROM of the KIM Clone.

List of changes to the original KIM-1 ROMs:

  1. Removal of the (6530-003) code to save/load from cassette tape.
  2. Lunar Lander (First Book of KIM) added.
  3. Farmer Brown (First Book of KIM) added.
  4. New X command from TTY to enter the Corsham Technologies xKIM extended monitor.
  5. L command also loads Intel hex file (from input, send file in terminal emulator, like you can do with papertape files)

There is no technical reason why you could not load the original KIM 6530-002 and 6530-003 ROMs into the KIM Monitor EPROM. The Corsham KIM Monitor is a bit more convenient.

Source of Corsham KIM Monitor

xKIM Monitor
Placed in the extra EEPROM

Extra commands in teletype mode.

  ? ........... Show this help
  D ........... Disk directory
  E xxxx ...... Edit memory
  H xxxx xxxx . Hex dump memory
  J xxxx ...... Jump to address
  K ........... Go to KIM monitor
  L ........... Load HEX file
  M xxxx xxxx . Memory test
  P ........... Ping disk controller
  T ........... Type disk file
  ! ........... Do a cold start

Source of Corsham KIM Monitor

Corsham eXtended KIM Monitor Manual
Source of Corsham KIM Monitor

Microsoft 8K BASIC
Download the original KB9 binary, dumped from official Micro-soft (no typing error, original name!) cassette audio tape, and documentation from this site.

Or build your own version from the pagetable blog (for which my KB9 was the KIM-1 version as input!) Install the CC65 package, then run the command, then look at the file tmp/kb9.bin, You’ll need to convert that raw binary image to a file suitable for downloading to the KIM, see the KIM-1 tools for a utility. All of these needs at least 12K of RAM starting at $2000 in the KIM-1

Binaries of KB9

Here is a file suitable for downloading onto a KIM-1. It loads at $2000 but to run it you’ll need to start at $4065. Use the L command in KIM-1’s monitor, then upload the file. I strongly suggest that you change your terminal emulator so it adds a 200 ms pause at the end of each line. Once it loads, run it by going to 4065 and running it.
4065 G
To see the easter egg, answer “A” when it asks for memory size.

Original KIM-1 Microsoft BASIC KB9

This is still experimental but I have a version which uses functions in the xKIM monitor (present on the KIM Clone or on the 60K RAM/EPROM board) to save/load from the SD Card System. It also has a DIR command. This is an Intel HEX file and must be loaded from the xKIM “L” command:

Download hex file xkim

This loads and runs at $2000.

Tom Pittman’s Tiny BASIC
Tom distributed a very small BASIC that needed about 3K to run, and was available on paper tape for $5!!! He has quite a bit about it at:

Here is the source code, listing, and binary to my disassembly which includes a lot of comments and notes from Tom Pittman:
Tiny Basic source
Tiny Basic listing

A ready-to-run binary which loads at $0200 and should have RAM up to $13FFL
Tiny Basic hex file

Bob’s Tiny BASIC
by Bob Applegate

All the early issues of Dr Dobb’s Journal discussed using using an intermediate language (IL) to write a general interpreter, then writing a BASIC interpreter using the IL language. Nobody used this except for Tom Pittman. I liked the idea and about five years ago wrote my own BASIC using that approach. It is buggy, but the sources are on the Corshams github so anyone can take them, hopefully debug things, and put fixes back in place. My version also has commands to save/load programs to/from a Corsham Technologies’ SD Card System.

Source and documentation of Bob’s Tiny Basic

And a binary version that can be run starting at address 0200

AS65 assembler

The software above was assembled with the AS65 Kingwoods assembler, a command line utility for Windows (including 10).

Download here AS65

A typical build for a bianry and hex output would be:

REM Build xKIM
as65 -l -s2 xKIM.asm
as65 -l xKIM.asm

Type “as65 ?” for help

Memory Test

by Bob Applegate
This memory test was originally based on Jim Butterfield’s memory test program in the First Book of Kim, but has grown a bit. This now tests every memory location using a rolling 9-bit pattern. Ie the pattern repeats every 9 bytes, so this will detect most shorted address line problems. I use this to test memory boards, so it will run forever unless an error is detected. At the end of each pass, a ‘.’ is printed.

This does output to the TTY port, so if you’re only using the default KIM display, the output functions will need to be tweaked. Not hard to do, but I didn’t need it.

Written February 2006 by Bob Applegate, but it uses some bits of code from Jim Butterfield, and Ross Archer
Memory test soource and hex file

Microchess Peter Jennings
Adapted for KIM clone by tennyson.neil

Source and hex file Microchess for the KIM clone


Corsham KIM Clone peripherals

KIM Clone Motherboard

KIM Clone Motherboard User Manual
KIM Clone Motherboard schematic

KIM Clone Proto Board

KIM Clone Proto Board User Manual

KIM Clone I/O board

KIM Clone I/O Board Manual
KIM Clone I/O board Rev 3 Schematic

KIM-1 I/O Board

KIM-1 I/O Board Manual
KIM-1 I/O Board schematic

KIM-1 60K RAM/ROM Board

KIM 60K RAM ROM Manual
KIM 60K RAM ROM Schematic

KIM Clone information

KIM Clone User Manual Rev 2
KIM Clone Rev 2 Circuit Diagram
KIM Clone User Manual Rev 5
KIM Clone Rev 5 Circuit Diagram
Building a KIM Clone, Tech tips

Fix for KIM Clone Single-Step Problem

Rev 1B and rev 2 boards have a problem where single-step mode does not work. It works for old 6502s but not for newer ones nor 65C02. The solution was very simple: add a .001 uf capacitor across U16 pins 7 and 8. All assembled KIM Clones now have the modification and future revisions of the board will have the capacitor on the motherboard.


Corsham SD card system

SD Card System.

This is a two board system that provides a very inexpensive, flexible, and long-lasting storage option for our KIM Clone , SS-50 based designs, or almost any third party system.

The main board is the Corsham SD Shield. It plugs into an Arduino Mega and provides for insertion of a micro SD card, and also includes a DS3231 based real time clock (RTC). The Arduino does the hard work of providing an interface between the host processor (6502, 6800, 6809, etc) and the SD card and RTC. It connects to the host via a ribbon cable.

The board also contains three LEDs used for status, a RESET switch, a four position DIP switch, a DS3231 RTC, backup battery, and it maintains the Arduino Mega headers so additional shields can be placed on top. Since the source code is available you can add additional drivers for whatever shields you add. Want to add an LCD shield that displays which files are mounted? Just plug in the shield and modify the user interface class in the source code. Only one of the DIP switches has a defined purpose, so the rest are free for you to add your own logic.

The protocol between the host and the SD Card System is completely defined in The Remote Disk Protocol Guide available for download below.

The source for the Arduino Mega is also available for download.

SD Card System manual
SD Card Schematic
SD drive Arduino November 2020 source
SD shield tester, set RTC time source Arduino
The Remote Disk Protocol Guide
6502 routines for KIM-1 low and high-level disk access
Also see xKIM extended KIM Monitor