A512
The A512 is a 512kByte trapdoor memory expansion for the A500 computer. 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
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. This 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+.
Contents |
Jumper settings
J1 switches the expansion ON. This jumper may also be used to connect a switch.
J2 is closed by default and may only be opened in one very rare case: If open, it leaves the RTC of an A500+ enabled, although there is a second 512k expansion connected to the pass-through of the A512. In most cases, the second 512k-expansion will switch off the internal RTC of the A500+ for safety reasons (there may not be more than one chip at the same address space!). However, if this second expansion has an empty socket for the RTC chip, it is safe to keep the RTC on the main board of the A500+ enabled. In this case (and only in this case!), you may open J2 to keep the RTC on the A500+ main board active. Installing an RTC module on the A512 will disable the RTC on the A500+ main board, regardless of the state of J2.
A512 revisions
A total of three different versions of the A512 have been made. Boards from the first production run have a small cut-out at the bottom left, which boards from the 2020 production run do not have. Further, the 2020 production run is split into two versions, where one version uses two additional low-power logic chips to make a certain type of memory chip compatible with the A500. This is an implementation detail that does not change the functionality of the expansion. Most people wouldn't even notice the difference, but if you do, this paragraph explains the slightly different appearance that your board may have from the pictures you see in our shop system, this Wiki or other sources on the internet.
Shop
- Individual Computers' Shop (selected Products)
Resellers
Please shop locally. Our partners are listed in alphabetical order.
- Alinea Computer (Germany)
- Amiga Kit (UK, US)
- F.H.U.EDEN Komputery (Poland)
- GGS Data (Sweden)
- Protovision (Germany) (Retro Products only)
- Relec Software & Hardware (Switzerland)
