- When WRAM ($6000-$7FFF) is disabled (writes are not allowed), what value does a dummy read return: $FF, $00 or the high byte of the read address? Yes, it's mapper-specific, but my memory fails about what mapper...
As I understand it, the capacitance of an open bus keeps the most recent voltages on the bus. Open CPU data bus on an authentic Game Pak is usually the high byte of the address, but it may differ when indexed addressing (a,x, a,y, or (d),y) crosses pages. PowerPak, on the other hand, doesn't really use an open bus because it has resistors to pull the voltages to a known value; this causes problems with poorly written controller reading functions in a few Mindscape games. And I think MMC5 has a mode where reads work but writes are ignored.
- Ah, yes, one case: the MMC3 (mapper 4).
Code:
=== PRG RAM protect ($A001-$BFFF, odd) ===
7 bit 0
---- ----
RWxx xxxx
||
|+-------- Write protection (0: allow writes; 1: deny writes)
+--------- Chip enable (0: disable chip; 1: enable chip)
- So, if the chip is disabled, what would a WRAM read return?