512K Trapdoor memory expansion and Real Time Clock for Amiga 500, 500+
This is a tested working project. I designed the board to accommodate the parts that I already had in stock that's why it uses SOJ package DRAMs instead of thru-hole ones. Any 256Kx4 DRAM should work on it, here is a comprehensive list of such DRAM ICs.
https://www.amiga-stuff.com/hardware/256kx4-dram.html
The diodes are not crucial and can be substituted with other ones with similar properties too, prefer the ones with as little voltage drop as possible. It is also possible not to populate the RTC part of the board if not required. In fact, the A500+ Rev 8 motherboard has its own RTC, so better not to populate that part is it is going to be used in a Rev 8 board.
All the part values are clearly indicated on the PCB silk layer, the resistors and ceramic caps are SMD size 0805. I recommend 16V rated electrolytic caps. For the 32.768 KHz RTC crystal, I have provided alternative pads for SMD and thru hole types, only one type should be populated.
This board will add 512KB RAM to any Amiga 500, but due to the chipset differences it will work as "Slow RAM" in motherboards up to and including Rev 5. For Rev 6 boards, depending on the board chipset, it will be configured as "Slow RAM" (OSC) or "Chip RAM" (ECS). It will be configured as "Chip RAM" in Rev 8 boards. There are no mods needed to be done on the motherboards, it will work plug & play.
512K Trapdoor memory expansion and Real Time Clock for Amiga 500, 500+
*PCBWay community is a shared platform and we are not responsible for any design issues.
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