AT91M40807 ATMEL Corporation, AT91M40807 Datasheet - Page 10

• Manufacturer Part Number: AT91M40807
• Description: At91 Arm(r) Thumb(r) Microcontroller
• Manufacturer: ATMEL Corporation

Abort Control
External Bus Interface
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AT91M40807
ory and the internal primary SRAM bank addresses. The remap command is accessible
through the EBI User Interface, by writing one in RCB of EBI_RCR (Remap Control
Register). Performing a remap command is mandatory if access to the other external
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
microcontroller 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 0 x 0040 0000
and 0 x FFC0 0000. It generates the signals that control access to the external devices,
and can be configured from eight 1M-byte banks up to four 16M-byte banks. It supports
byte-, half-word- and word- aligned accesses.
For each of these banks, the user can program:
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The External Bus Interface also features the Early Read Protocol, configurable for each
device, that significantly reduces access time requirements on an external device in the
case of single-clock cycle access.
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).
1371CS–ATARM–02/02