rosco_m68k RAM expansion

The RAM expansion adds four megabytes of static RAM to the rosco_m68k. It plugs onto the 2×32 expansion pins of the main board or of a bus board slot, and the firmware counts the extra memory at boot.

• Memory: 4 MB of static RAM, eight AS6C4008 chips of 512 KB each
• Decoder: a programmed ATF16V8 that places the card in the address map
• Base address: 1 MB to 13 MB, set by three jumpers. With all three open the card starts at 1 MB, right after the main board's memory
• Board: 122 × 104 mm, through-hole parts only, chips in sockets
• Main board: rosco_m68k r2, with JP4 on the main board shorted: the main board answers the CPU for the card

Build it#

The build guide takes you from a bare PCB to a memory count at boot in five soldering stages, with a board map for every stage. It is also available as a PDF to print.

Reference#

• Address jumpers and memory map: JP4 on the main board, the JP1–JP3 base address, and several cards in one system
• How it works: the decoder, the memory chips and the signals the card uses
• FAQ: short answers to the most common questions

The rosco_m68k RAM expansion is open-source hardware by Ross Bamford and contributors (rosco-m68k.com), released under the CERN Open Hardware Licence.