INES Mapper 243

iNES Mapper 243 describes Sachen's “74LS374N” mapper IC, which in no way resembles its namesake.

Unfortunately, it seems that there are several different ways this board was wired. Submappers may need to be allocated.

The IC, as described by Санчез, and as images in GoodNES, does not have any games with more than 64KiB PRG, so it's unclear why Nestopia or Санчез specify three bits for PRG banking.

 Example Games:
 --------------------------
 Honey
 Poker III 5-in-1
 
 Registers:
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 Mask: $E101
 
   $4100:  [.... .AAA]   Address for use with $4101
 
 Variant one (Nestopia calls "374b" and refiles to iNES Mapper 150, but what Санчез specified) :
   $4101:   Data port
      R:2 -> [.... ...B]  High bit of CHR reg AND ALSO sets PRG reg to B.
      R:4 -> [.... ...C]  Middle bit of CHR reg
      R:5 -> [.... .PPP]  PRG reg  (32k @ $8000)
      R:6 -> [.... ..DE]  Low bits of CHR reg
      R:7 -> [.... .MM.]  Mirroring
          %00 = Horz
          %01 = Vert
          %10 = L-shaped; see below
          %11 = 1ScA

    Nestopia asserts that both addresses are readable and return the inverted value of AAA, possibly XORed with some some unique ID.
 
  Variant two (Nestopia calls "374a" and leaves as mapper 243, what Nocash specified) :
   $4101:   Data port
      R:0 -> [.... ....]  Writes reset CHR bank to 3 and PRG bank to 0
      R:2 -> [.... ...B]  High bit of CHR reg
      R:4 -> [.... ...E]  Low bit of CHR reg
      R:5 -> [.... ...P]  PRG reg  (32k @ $8000)
      R:6 -> [.... ..CD]  Middle bits of CHR reg
      R:7 -> [.... ...M]  Mirroring
           0 = Horz
           1 = Vert
 
 Mirroring:
 ---------------------------  
 Mirroring mode %10 is not quite 1ScB:
   [  NTA  ][  NTB  ]
   [  NTB  ][  NTB  ]
 
 CHR Setup:
 ---------------------------  
 8k CHR page @ $0000 is selected according to some permutation of the BCDE bits.

Of all the images marked as mapper 243 in GoodNES 3.1.4, Nestopia's database leaves ONLY Poker III (Sachen) [!] and Poker III (Sachen) [a1].nes as variant 374a, and refiles the rest as variant 374b.

There are two different dumps of "Poker III" in GoodNES, both marked with [!]. This has caused some confusion. There is no difference in the PRG of these two images! The only difference seems to be the different interpretation of CHR order. Given that Санчез described the pinout, and so presumably actually figured out which pin connected to which pin on the ROMs, it seems not unlikely that all of GoodNES (and No-intro)'s "authoritative" dumps may be wrong.

This still doesn't address the difference in mirroring behavior. Nocash says that no game ever wrote anything other than $05 to the register anyway.

Reference: Санчез ( http://cah4e3.shedevr.org.ru/%5Blst%5D-sachen-mappers.txt ), Nestopia's source, Nocash