AT91M40807 データシートの表示（PDF） - Atmel Corporation

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AT91M40807

AT91 ARM® Thumb® Microcontrollers

Atmel Corporation 

Chip Select Lines

AT91X40 Series

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 external 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

following 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 7. Memory Connections for Four External Devices

NCS0 - NCS3

NRD

EBI

NWRx

A0 - A23

D0 - D15

NCS3

Memory Enable

NCS2

Memory Enable

NCS1

Memory Enable

NCS0

Memory Enable

Output Enable

Write Enable

8 or 16

A0 - A23

D0 - D15 or D0 - D7

Note: For four external devices, the maximum address space per device is 16M bytes.

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1354D–ATARM–08/02

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