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6174B–ATARM–07-Nov-05
AT91FR40162S Preliminary
10.3
Chip Select Lines
The EBI provides up to eight chip select lines:
• Chip select lines NCS0 - NCS3 are dedicated to the EBI (not multiplexed).
• Chip select lines CS4 - CS7 are multiplexed with the top four address lines A23 - A20.
By exchanging address lines for chip select lines, the user can optimize the EBI to suit the exter-
nal memory requirements: more external devices or larger address range for each device.
The selection is controlled by the ALE field in EBI_MCR (Memory Control Register). The follow-
ing combinations are possible:
A20, A21, A22, A23 (configuration by default)
A20, A21, A22, CS4
A20, A21, CS5, CS4
A20, CS6, CS5, CS4
CS7, CS6, CS5, CS4
Figure 10-2. Memory Connections for Four External Devices
Note:
For four external devices, the maximum address space per device is 16M bytes.
Figure 10-3. Memory Connections for Eight External Devices
Note:
For eight external devices, the maximum address space per device is 1M byte.
EBI
NCS0 - NCS3
NRD
NWRx
A0 - A23
D0 - D15
NCS3
NCS2
NCS1
NCS0
8 or 16
Memory Enable
Memory Enable
Memory Enable
Memory Enable
Output Enable
Write Enable
A0 - A23
D0 - D15 or D0 - D7
EBI
NCS0 - NCS3
NRD
NWRx
A0 - A19
D0 - D15
CS7
CS6
CS5
CS4
8 or 16
Memory Enable
Memory Enable
Memory Enable
NCS3
NCS2
NCS1
NCS0
Memory Enable
Memory Enable
Memory Enable
Memory Enable
Memory Enable
Output Enable
Write Enable
A0 - A19
D0 - D15 or D0 - D7
CS4 - CS7