AT91M40800(2002) データシートの表示（PDF） - Atmel Corporation

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AT91M40800
(Rev.:2002)

AT91 ARM® Thumb® Microcontrollers

Atmel Corporation 

Abort Control

External Bus Interface

devices (connected to chip-selects 1 to 7) is required. The remap operation can only be

changed back by an internal reset or an NRST assertion.

The abort signal providing a Data Abort or a Prefetch Abort exception to the ARM7TDMI

is asserted when accessing an undefined address in the EBI address space.

No abort is generated when reading the internal memory or by accessing the internal

peripherals, whether the address is defined or not.

The External Bus Interface handles the accesses between addresses 0x0040 0000 and

0xFFC0 0000. It generates the signals that control access to the external devices, and

can be configured from eight 1-Mbyte banks up to four 16-Mbyte banks. It supports

byte-, half-word- and word-aligned accesses.

For each of these banks, the user can program:

• Number of wait states

• Number of data float times (wait time after the access is finished to prevent any bus

contention in case the device is too long in releasing the bus)

• Data bus-width (8-bit or 16-bit).

• With a 16-bit wide data bus, the user can program the EBI to control one 16-bit

device (Byte Access Select mode) or two 8-bit devices in parallel that emulate a 16-

bit memory (Byte Write Access mode).

The External Bus Interface features also the Early Read Protocol, configurable for all the

devices, that significantly reduces access time requirements on an external device in

the case of single-clock cycle access.

10 AT91M40800

1348DS–ATARM–02/02

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