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MAD-1 connections on 1A3M-30 PCB - confused


Original poster
Jul 16, 2019
AG Join Date

For my own education purposes I have been using my multimeter to map out a bunch of different PCBs. I have a copy of Black Bass III (Jap) which uses a 1A3M-30 PCB. Here is the pinout of the MAD-1 as I can tell with my meter:

X---------|1 {/RomCS1}  {/RomCS0} 16|---------X
SRAM /CS1-|2 {/SramCS}    {Addr0} 15|-------A15
X---------|3 {/AuxCS}     {Addr1} 14|-------A20
ROM /OE---|4 {/RomCS}     {Addr2} 13|-------A21
SRAM Vcc--|5 {Vout}       {Addr3} 12|-------Vcc
Vcc-------|6 {Vcc}        {/CART} 11|-----/CART
R1--------|7 {Vbat}        {MODE} 10|-------GND
GND-------|8 {GND}       {/RESET}  9|----/RESET

Notice Addr3 is connected to Vcc, in my experience this is normally connected to A22 since that maps the Sram correctly to $70-7D,$F0-FF:$0000-7FFF. However, unless I am completely mistaken, if we connect Addr3 to Vcc won't we be also mapping Sram to $30-3F,$B0-BF:$0000-7FFF (since we don't care about A22 any more)? This area is reserved for all sorts of stuff so why would the cart map the Sram here?

Is it something to do with the fact that this is a 32Mbit ROM? There is some weirdness with LoRoms of this size since the last bit of ROM cannot be accessed in the lower half of the memory map (because WRAM is mapped in the 7E-7F banks I think) so you have to look for it in the upper mirror (FE-FF).

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