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Supporting hardware, expansions and projects for the rosco_m68k

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Incorrect RAM Expansion Decode for Huge ROM IC2

0xTJ opened this issue · comments

commented

The current Huge ROM IC2 only decodes /EXPSEL for $00100000 to $001FFFFF, instead of all the way to $00DFFFFF.

hardware-projects/flash-rom/code/pld/huge_address_decoder/ic2_address_decoder.pld

Line 17 in 72f1783

/EXPSEL = IACK * /AS * /A23 * /A22 * /A21 * A20 

-/EXPSEL       = IACK * /AS * /A23 * /A22 * /A21 * A20
+/EXPSEL       = IACK * /AS * A23 * /A21
+              + IACK * /AS * /A23 * A22
+              + IACK * /AS * /A23 * A20
+              + IACK * /AS * /A22 * A21

I noticed it when Mosys RAM expansion scan would cause a bus error at $00200000. I got the PLD address equations from a truth table -> logic equation tool, so I've hopefully gotten that right. It now gets through the entire expansion space without a bus error.