Memory map
(This section was taken from Joe's page..) 

The HuC6280 has a 64KB logical address space and a 2MB physical address space. To access this entire memory space, the processor depends on 8 memory mapping registers, known as MPR0 - MPR7. These registers map each 8KB segment of the logical address space to an 8KB segment in the physical address space. The first segment of a HuCard will be mapped to $E000, and the first instructions map segment $FF to $0000 and segment $F8 to $2000. When the Savegame RAM is present, it should be mapped to $8000. 

The Instructions for accessing the zero-page or the stack will always work on segment F8. 

Segment # Description  
FF IO-ports  
F8-FB Base RAM SuperGrafx (32KB)  
F8 Base RAM normal PC-Engine (8KB)  
F7 Savegame RAM  
00-F6 HuCard storage  

The Interrupt-Vectors are taken from them bank, that is mapped to $E000. One example is the "NES-Collection" ROM, which maps another bank to this address for each game. Only the Reset-Vector is always taken from ROM-bank #0. 

$FFFE-$FFFF Reset Vector  
$FFFC-$FFFD NMI Vector  
$FFFA-$FFFB TIMER Vector  
$FFF8-$FFF9 IRQ1 Vector (for VDC)  
$FFF6-$FFF7 IRQ2 Vector (for BRK)