Build your own

I put both the software and PCB hardware on my GitHub account. You can access them here:

How to build your board

The PCB of the board has 4 layers to make it smaller and fit into the small space inside the low-profile CBM-II machines. I am using to make my boards.

The board contains an Atmel ATF1508 CPLD chip. You need a suitable programmer, such as ATF15xx-DK2, to program the chip. The board has a JEDEC connector which can be used to connect to the programmer directly. Use the cobalt.jed file from the repository to program the chip.

There are two ROM images in the archive which are necessary for the card to work:

  • 8088.bin – 27C512 chip image to be placed at U7D
  • 6509.bin  – 27C64 chip image to be placed at U2C

There are also chargen_lp.bin and chargen_hp.bin images which can be used to replace the character ROM in your machine (respectively for low-profile and high-profile machines). They contain an alternate character set with some characters that are useful when running DOS (such as the backslash character). The card must be configured to use this character set – press F10 after booting the card to change the display configuration.

The archive contains an image of a bootable FreeDOS hard disk. Put this image onto an SD card that is at least 8 GB of size (there are several SD card imaging applications available, I am using Win32 Disk Imager). After writing the images, the SD card will be readable on your PC, so you can easily add other applications. Note that you must use this image to boot the 8088 card, because the SD card needs to be formatted with special CHS geometry for the INT 13h functions in the 8088 BIOS.

The ROM image from the repository contains the current version of the PC compatibility library. If you want to update the library in the future, grab the file from the repository, put it on the SD card and run it in DOS – it will write the newest version to the EEPROM chip on the board.