AT91M40400 데이터 시트보기 (PDF) - Atmel Corporation

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AT91M40400

AT91 ARM® Thumb® Microcontrollers

Atmel Corporation 

AT91M40400

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 his external memory require-

ments: 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 6. 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: 1. For four external devices, the maximum address space per device is 16M bytes.

Figure 7. Memory Connections for Eight External Devices

CS4 - CS7

NCS0 - NCS3

NRD

EBI

NWRx

A0 - A19

D0 - D15

CS7

Memory Enable

CS6

Memory Enable

CS5

Memory Enable

CS4

Memory Enable

NCS3

Memory Enable

NCS2

Memory Enable

NCS1

Memory Enable

NCS0

Memory Enable

Output Enable

Write Enable

8 or 16

A0 - A19

D0 - D15 or D0 - D7

Note: 1. For eight external devices, the maximum address space per device is 1M byte.

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