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Acorn Atom snow stopper
During my third bout of Acorn Atom-ing (my original purchase circa 1980, and two revisits beginning 2010 and 2022), I started investigating the 'snow' issue the Atom has always suffered from (which occurs due to contention between the 6502 and 6847 accessing 'video memory' (0x8000 - 0x97FF)).
Looking at existing 'fixers', it seemed to me that they had missed a pretty obvious solution : dual-ported SRAM. It turned out to be an excellent idea, because all the required signals were already there, on IC27-29. Zero glue logic needed (which was even more surprising). Just replace IC27-30 with a board.
Added bonus : 2 KB more 'high' RAM (0x9800 - 0x9FFF), and overclockable without effort (4 MHz and up).
View the result below. The capacitors are 10uF (case B, here : AVX TAJB106K010R) and 100nF (0805, here : Vishay VJ0805Y104KXAT), the chip is an IDT7005 (TQFP, here : IDT7005S35PFG).
You can download the Gerber files for the PCB here, and make your own.
First published 22 March 2025.
Acorn Atom snow stopper (top)
Acorn Atom snow stopper (bottom)
Acorn Atom snow stopper (installed)
Acorn Atom snow stopper (schematic)