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The CPU280 is a single-board ECB-interface computer based on the Z280 microprocessor from Zilog, designed and originally manufactured by Tilmann Reh in the early 1990's. The CPU280 runs the Z280 in the Z-BUS mode with a 16-bit data bus. 512KB, 1MB, 2MB, or 4MB of dynamic RAM can be installed. The system boots to CP/M+ from EPROM. The CPU280 was one of the very few hobbyist-buildable Z280 CP/M computers ever made. RBC forum member fritzeflink maintains an archive of information about the CPU280 at his site

Late in 2016, RBC forum member lowen contacted Tilmann Reh and obtained permission to have a new run of boards made. Tilmann very graciously provided the manufacturing files as well as all necessary documentation and source code to rebuild the system, and lowen was able to get a beta run of ten boards made and distributed to several beta builders. RBC forum member Wayne W developed a build setup to rebuild the EPROM images and floppy disk images and set up a github at for distribution and development. Several boards were successfully constructed using the beta run, and lowen had another ten boards fabricated. In spring 2018, another ten boards were run.

Tilmann Reh has given blanket permission for unmodified redistribution of the CPU280 files. Tilmann requests notification if the design is modified. Quoting his emailed permission, received by Lowen on 1/10/2017:

For me it's OK to distribute all of the CPU280 stuff (including the gerber files, the PDFs and the software) freely - as long as the design is not modified without my expressed permission.

The original design files in Eagle .BRD format ( ) are available as well. Here is what Tilmann has to say about the way Eagle was used in the early 1990s:

Take care that in the 90s, there was no schematic editor in EAGLE. Instead, i just drew the schematic with the board editor. So now you need to edit both files to keep them synced. (I include the “schematic” file so you can update your documentation/PDF according to the patched PCB.)

So the schematic is also a .BRD file and was drawn in the layout editor of Eagle.

Hardware Documentation

Board and Schematic: :boards:sbc:cpu280:cpu280_hardware-manual_en.pdf

Manufacturing Files:

KiCAD Files: Tilmann's original Eagle .BRD files are: Translation to KiCAD is not planned at this time; volunteers to do this are welcome!

Build Information

<Include thinks like parts lists, BOMs, test software, notes from the board designer, etc in this section.>

Builder's Notes/Comments

Please use this space to add any notes/comments on this board that don't fit into the above sections. (Periodically, these comments may be re-arranged to be better incorporated into a new revision of the wiki page.) Please sign your comments using the wiki “Insert Signature” feature! — Andrew Bingham 2016/02/27 13:01

The following are notes from my build — Richard Edwards 2019/08/10 16:32


The first LED goes off after reset

Middle LED stays lit if the battery in the DS1287/DS1287A is flat otherwise it goes out.

You can fix a flat battery in a DS1287 using a technique like the following Although it looks drastic IMHO you have nothing to lose by doing this modification to make the chip usable again.

LED closest to the CPU stays on while the memory test is occurring. Once it goes off the memory test is completed.


Best suggestion is to build new ROM's from the source per the link up the page. However if you need you can also use the v1.20.3 zip in the files section. Note I suspect that if you have version 1.20.1 ROM's then your board will not be showing anything on the serial console. I had the same issue and read in the very long forum thread about the CPU280 that someone worked out that the board was trying to display console on a graphics adapter that doesn't exist.

I had issues with the ANSICON in the git respositry so I downloaded the latest from here


Take a look at the PDF and make sure that you have BCE in the right location. Sometimes the board silk screen may not match the transistor pin out. If you look at some of the uploaded photos you can see the differences in peoples builds.

Serial Cable

The following cable worked for me. You then connect the CPU280 to a terminal via a null modem cable.

CPU280 BoardDB9 PIN Male
1 - GND5
3 - TXD3
5 - RXD2
7 - RTS7
9 - CTS8

I always find this link useful to work out what serial pin does what


I found the Jumpers zip file in the forum threads and have uploaded it here. Gives a very good description of what each one does.

Sample Boot Output

This is what I get on the console when it boots. I used setup to set my boot drive to Q which is the EPROM.

CPU280 Boot Loader V1.2 RBC 8-Mar-2017
based on Cold Loader Program V1.13 TR 950314
Press DEL to run SETUP.
2048k RAM ok

CP/M-3 Loader V1.2 RBC 8-Mar-2017
based on CP/M-3 Loader V1.13
Booting system file from EPROM

BNKBIOS3 SPR D000 2000
RESBDOS3 SPR F800 0600


CP/M-3 BIOS V1.2 RBC 8-Mar-2017
based on CP/M-3 BIOS V1.13 TR 950314

E: MDrive 3840k


happy building — Richard Edwards 2019/08/10 16:40

Nothing was found.

File List

FilenameFilesizeLast modified
2n3904.pdf166.8 KiB2019/08/10 02:27
cpu280-1.20.3.zip1.5 MiB2019/08/10 02:28
cpu280-eagle.zip61.9 KiB2018/06/26 09:00
cpu280-v1.20.1.zip684.0 KiB2017/05/26 14:21
cpu280-v1.20.2.zip1.4 MiB2017/08/01 00:22
cpu280_hardware-manual_en.pdf595.2 KiB2017/05/26 13:34
cpu280_software-manual_en.pdf395.4 KiB2017/05/26 13:34
jcoffman-1.jpg149.1 KiB2017/05/26 14:23
jcoffman-2.jpg189.8 KiB2017/05/26 14:23
lro-board-201612-1.jpg6.0 MiB2017/05/26 14:23
reh-cpu280-lro-2016-1.jpg4.9 MiB2017/05/26 14:23
reh-cpu280-lro-2016-web.jpg106.2 KiB2017/05/26 14:17
wayne-w-1.jpg1.8 MiB2017/05/26 14:23
z280-e5-gerber.zip55.0 KiB2017/05/26 13:33
z280_jumper_information.zip1.5 MiB2019/08/10 02:27
z280_reh.pdf1.4 MiB2017/07/05 15:38
boards/sbc/cpu280/start.1565504755.txt.gz · Last modified: 2019/08/11 02:25 by trick-1
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