KIM-1 Clone

A KIM-1 clone build by Bob Applegate of Corsham technologies.

Somewhat inspired by the microKIM by Vince Briel, who was inpired by Ruud Baltissen! The idea is replace the 6530’s with 6532 and by carefull memory decoding have the I/O, timer and RAM of the 6532s appear at the same locations as the 6530-002 and -003. ROM is added with an EPROM.

Not an exact copy, the ROM has been changed/enhanced with a KIM Monitor by Bob, though the original KIM-1 ROM should work also.

Available assembled and tested or as a kit. I have bought the PCB and plan to build it!


The Digital Group 6501 CPU board

The short-lived 6501 by MOS Technology appeared as far as I know only in a board made by The Digital Group.

Aroudn 1975 The Digital Group created their new, reasonably priced, multiple-board computer system with these advanced features:
– Intel 8080, Motorola 6800, or MOS 6500 CPU card
– video display/cassette interface card
– 8-bit parallel input/output ports
– 2KB dynamic memory
– The 3-board Intel or Motorola CPU kit cost $425, while the MOS 6500 CPU kit cost $375. Later, the Zilog Z-80 CPU was added to the selection for $475.

The Digital Group didn’t just copy the MITS Altair design as others did, they improved upon it, with features not available in other systems. For one, the DG system loads the Operating System from the cassette drive automatically with little user interaction. Additionally, the DG system was available with four different CPU cards – the rest of the system remains fully compatible, no matter what CPU card was installed. Technically, the DG system has three different buses for CPU, memory, and I/O. Because of this, the card slots are different sizes and dedicated to each card type:


 650X CPU card construction PDF
 650x Operating system PDF, with listing in octal!


MPS-65 CT-65 Thaler

Thaler AG is a German company, still in business. Around 1983 the company sold a 6502 development system in the format of a SBC, size 2x Euroboard, and several enhancements for it under the name CT-6502 or CT-65. 6502 based, hex keyboard and the usual 6 seven segment LED displays, audio cassette storage.

In 1984 a smaller and stripped version SBC was produced, named MPS-65, size Euroboard. Accompanied by add-on boards such as VIA board and cassette interface. Same software, same keyboard and displays, more modern technology, no cassette storage, less ROM sockets.

In the German magazine MC adverts and articles were published in 1983 and 1984 (thanks user GaBuZoMeu on, shown here:


CT-6502 or CT-65

A SBC in the KIM-1 style. Keyboard with 24 keys, 6 seven segment LED displays, simple audio cassette storage, 1 K RAM, 2 K EPROM, some empty IC sockets.


A rare 6502 SBC. Only two have been seen by me. One is shown by user mba on the forum at, who also dumped the system ROM in EPROM. The other was shown on the Facebook group “6502 Homebrew Hardware and Programming” by user Ian Day. who build this system in the 80ties. The MPS65 is a stripped down version of the CT-65, missing ROM sockets and audio cassette storage.

The Euroboard sized SBC has a 6-digit LED display, a 24 keyboard with hex keys and several function keys. Requires a stabilized power supply 5V.  WIth expansion connector 64 pins, Siemens SMP bus compatible. On the board is written MPS 65-2. At the bottom of the inscription Thaler  (the same inscription is in ROM, in addition to the date 1984.

“MPS 65-2”, “THALER” and “85-1-1” are labels on the CPU board (mba system). The ROM contains (C)BY THALER1/1984

MPS 65-2 owned by mba

Ian Day system

Address selection MPS-65

Ian supplied a dump of the still operational 82S126 PROM.

addr B addr D Output.
00000000 -> 0 -> 1011
00000001 -> 1 -> 1011
00000010 -> 2 -> 1011
00000011 -> 3 -> 1011
00000100 -> 4 -> 1011
00000101 -> 5 -> 1011
00000110 -> 6 -> 1011
00000111 -> 7 -> 1011

10100000 -> 160 -> 1101

11110000 -> 240 -> 0111
11110001 -> 241 -> 0111
11110010 -> 242 -> 0111
11110011 -> 243 -> 0111
11110100 -> 244 -> 0111
11110101 -> 245 -> 0111
11110110 -> 246 -> 0111
11110111 -> 247 -> 0111
11111000 -> 248 -> 0111
11111001 -> 249 -> 0111
11111010 -> 250 -> 0111
11111011 -> 251 -> 0111
11111100 -> 252 -> 0111
11111101 -> 253 -> 0111
11111110 -> 254 -> 0111
11111111 -> 255 -> 0111

Output 4 is Rom (16  pages, 8 would be enough for 2716, optional 4K 2732?), three is Ram (8 pages, 2K SRAM 6116) and two is VIA 6522, one page .
Note that the CT-65 has a different PROM and four chip select lines are generated, see the manual.

Memory map MPS-65 and CT-65

0000 RAM,  6116 2K (2x 2114 on CT-65)
A000 6522
E000  and E003 addresses are called by routines in the system ROM. The ROM socket for ROM at E000 are not present on the MPS-2, only on the CT-65.
F800 ROM, 2K 2716

Requires a stabilized power supply 5V


A 1 (mba system) or 2 (Ian Day) MHz crystal delivers the clock.  CPU can be 6502 (mba) or 65C02 (Ian Day)

Power on Reset

A transistor a capacitor and resistor (and the 74LS00) drive the power on reset.

LED and Keyboard

A VIA 6522 supplies I/O for the keyboard/LED display. The darlington array ULN2003 (mba system)  or RS307-109 (Ian Day) is driven from the 6522 and goes through limiting resistors and up to the 7 individual segments of the LEDS. So this drives the rows of the display. 6 transistors drive the columns.

RAM is 6116 SRAM, supplyinf zero page, stack and the RAM for user programs at $0200. The CT-65 uses 2 2114 for 1K RAM

ROM is 2K 2716 at $F800  (memory decode may point to 2732 support). Empry IC sockets on the CT-65 for E000-F7FF

System Rom

The MPS-2 and CT-65 systems seem to share the same system ROM. Some functions can not be used on the MPS_2 such as Load and Save due to missing hardware.

User mba made a dump of the MPS-2 sytem ROM. Binary file here, in hex format here. In theory this is the same system ROM as the CT-65 uses. From the magazine article I read that an updated version for the CT-65 was developed, it is safe to assume this updated version is also used for the later MPS-65.

A disassembly has been made by me, see the assembler source here 
Not too much comments yet. The jumptable at the start has been filled in with information found in the manual. Not yet tried to assemble the source!

Ian Day also disassembled his ROM of the MPS-65 and it is different in subtle ways, see it here. And here the dump of his ROM.


From the video above an attempt has been made to reconstruct the manual of the CT-65, available as PDF here. The manual contains a description of the extensive commands available on the keyboard, circuit diagrams and other interesting facts. A source listing of the system ROM has never been published, only the jumptable is documented in a very terse format.