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1745D–ATARM–04-Nov-05
AT91M55800A
7.7 External Bus Interface
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
configure up to eight 16-Mbyte banks. In all cases 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.