A512 KB memory expansion for A500(+)

The A512 is our interpretation of a 512kByte trapdoor memory expansion for the A500 computer. This means that it's not just yet another copy of a product that was available from lots of second-source manufacturers during the late 1980s and 1990s, but it is looking at the needs of all A500 owners today:

• 512k RAM
• pass-through port for use in Amiga 500+
• space for an RTC module
• compatible with ECS Agnus types for Chipram expansion
• safe operation with OCS Agnus 8370 and 8371

Today's collectors and computer restoration experts like to keep a separate computer with a full OCS chipset and just a trapdoor memory expansion for the classic 0.5M Chipram and 0.5M ranger-mem configuration. With many second-source memory expansions using megabit memory chips, the setup will tend to run unstable, because the OCS Agnus types 8370 and 8371 will not generate enough refresh-addresses for most trapdoor memory expansions that use less than 16 memory chips.

Our A512 memory expansion will run properly with all Agnus types, including OCS chips. Thanks to an additional refresh circuit, the single 4MBit memory chip will get enough refresh addresses to keep it's contents in any configuration.

When operated in an A500+ computer, the A512 will be used as Chip ram, and two of these expansions can be cascaded to reach the maximum configuration of 2MBytes graphics memory (1 MByte on the main board, and 1 MByte in the trapdoor slot). The pass-through port is compatible with any other 512k trapdoor expansion, as long as it fits mechanically. The A500+ on-board RTC is only switched off if the RTC module has been installed on the A512 card.

The A512 memory expansion is compatible with all motherboard revisions from Rev.3 to Rev.8, including the A500+.