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Ext. FLASH 256K
FPGA res.
FPGA res.
Ext. RAM 512K
FLASH - image of
FF4000-FFFFFF
Peripheral
External
Int. RAM 6K
External-FPGA
Peripheral
External bus mode with MIRROR on
(SWAP off)
The address decoding and memory chip selects generation is done in the FPGA.
Since the Devkit16 Mainboard can be delivered with external SRAM memories
of 512K or 2M size, the FPGA decodes the address in a way that it reserves a
2M block in both the high memory block (HMB, 800000H-FFFFFFH) and
lower memory block (LMB, 010000H-800000H). In the LMB it is the
100000H-2FFFFFH area, in HMB it is E00000-FFFFFF. With the 512K version
of the Mainboard, the SRAM memory will therefore be mirrored in these areas
four times and the 256K FLASH eight times. For example, accessing address
100000H will do the same as address 180000H, 200000H and 280000H in the
SRAM memory (SWAP is off). Also, addresses E00000H, E40000H, E80000H
and so on will work the same for the 256K FLASH memory.
This allows using the whole 256K of FLASH (or 512K of SRAM when SWAP
is ON) in the mixed mode, when there is the internal FLASH on addresses
FC0000H-FFFFFFH - the external memory can be accessed on lower addresses
in the 2M block, e.g. E00000H.
The Adr/IO switch allows to use the A16-A23 CPU pins as a general I/O mode
pins. If the switch is on, any memory access above the 00FFFFh address is
mirrored to the 4000h-FFFFh area. The decode logic (FPGA) ignores the A16-
A23 address signals and the MirrorFF bit setting. This switch allows to use the
port P2 (A16-A23 signals) as general I/O without giving up the external
RAM/FLASH memory. It can be useful for developing mixed mode
applications with only one 64k external RAM memory bank, that need more I/O
FFFFFFH
FC0000H
E00000H
2FFFFFH
180000H
100000H
00FFFFH
004000H
003900H
002000H
0018FFH
000100H
0000BFH
000000H
External bus mode with MIRROR on
76
76
76
76
Ext. RAM 512K
FFFFFFH
F80000H
FPGA res.
E00000H
2FFFFFH
FPGA res.
140000H
Ext. FLASH 256K
100000H
FLASH - image of
00FFFFH
FF4000-FFFFFF
004000H
Peripheral
003900H
External
002000H
0018FFH
Int. RAM 6K
000100H
External-FPGA
0000BFH
Peripheral
000000H
and SWAP on
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