MPS-65 CT-65 CT-6502 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:



(video by the previous owner, Cristian)

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

Manual and ROM dump

Thaler CT-1065 manual
ROM dump ROM dump (2732, only upper 2K have code)

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 entry points are documented in the (enhanced) manual.


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, supplying 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.

Ian Day designed a clone of the MPS-65. All design files here at Easy EDA

Replacement of some old prom by a GAL, Application to a Thaler MPS-65 board

Didier form was approached by his friend Erik about a malfunctioning MPS-65.

By studying the material on this page and doing measurements on the board it was decided the PROM on the board was malfunctioning.

So Didier designed a GAL replacement for the PROM and the board came back to life!

Here the story how the design looks like.