at91sam9g20-cu ATMEL Corporation, at91sam9g20-cu Datasheet - Page 159

• Manufacturer Part Number: at91sam9g20-cu
• Description: At91 Arm Thumb Microcontrollers
• Manufacturer: ATMEL Corporation

21.6
Figure 21-2.
21.7
21.7.1
21.7.2
6384B–ATARM–15-Dec-08
External Memory Mapping
Connection to External Devices
Data Bus Width
Byte Write or Byte Select Access
SMC
Memory Connections for Eight External Devices
NCS[0] - NCS[7]
D[31:0]
A[25:0]
NWE
NRD
The SMC provides up to 26 address lines, A[25:0]. This allows each chip select line to address
up to 64 Mbytes of memory.
If the physical memory device connected on one chip select is smaller than 64 Mbytes, it wraps
around and appears to be repeated within this space. The SMC correctly handles any valid
access to the memory device within the page (see
A[25:0] is only significant for 8-bit memory, A[25:1] is used for 16-bit memory, A[25:2] is used for
32-bit memory.
A data bus width of 8, 16, or 32 bits can be selected for each chip select. This option is con-
trolled by the field DBW in SMC_MODE (Mode Register) for the corresponding chip select.
Figure 21-3
connect a 512K x 16-bit memory on NCS2.
as a single 32-bit memory
Each chip select with a 16-bit or 32-bit data bus can operate with one of two different types of
write access: byte write or byte select access. This is controlled by the BAT field of the
SMC_MODE register for the corresponding chip select.
shows how to connect a 512K x 8-bit memory on NCS2.
8 or 16 or 32
NCS0
NCS1
AT91SAM9G20 Preliminary
Figure 21-5
NCS2
A[25:0]
Memory Enable
Output Enable
Write Enable
D[31:0] or D[15:0] or
D[7:0]
NCS3
Memory Enable
Figure
NCS4
Memory Enable
NCS5
shows two 16-bit memories connected
NCS6
Memory Enable
21-2).
NCS7
Memory Enable
Memory Enable
Memory Enable
Figure 21-4
Memory Enable
shows how to
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