AT91SAM7A2-AI datasheet(27/369 Pages) ATMEL

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PRELIMINARY

AT91SAM7A2

6021A–ATARM–07/04

External Memory Device

Connection

Each chip select can operate with one of two different types of write access by setting

the Byte Access Type bit.

Byte select access (BAT = 1): uses one write signal, one read signal, and two

signals to select upper and lower memory bank (used for SRAM) in a 16-bit

memory.

Typically used with 16-bit memories, except when user want to connect 2x8-bit

memories in parallel, in that case seen by the AMC this is a 16-bit memory.

Byte write access (BAT = 0): uses two write signals for selecting two different

8-bit memories and a read signal.

Typically used with 2x8-bit memories, this mode is used at reset to boot on the

memory connected on NCS0 (Chip Select 0).

Byte Select Access (BAT = 1)

This mode is selected by setting the BAT bit to 1 in AMC_CSRX registers and is typi-

cally used to connect the EBI with a 16-bit memory. All 2X8-bit memories can be

connected in this mode.

Users can use the upper/lower bank selection signal to get either an 8-bit or a 16-bit

access.

The signal NOE is used for reading and the signal NWE is used for writing. Signals NUB

(upper bank selection) and NLB (lower bank selection) are used to have a 8-bit access.

The following illustrations Figure 9, Figure 10 on page 28 and Figure 11 on page 28

show how to connect a typical 16-bit memory and 2x8-bit memories with 16-bit access

and a 16-bit memory with 8-bit access.

16-bit Access Device

Connection

A typical 16-bit memory (e.g. Flash) device connection with 16-bit access is listed below,

NLB and NUB are not used.

•

The A0/NLB signal is not used

•

The NWR1/NUB signal is not used

•

The NWR0/NWE signal is used as NWE and enables half-word writes.

•

The NRD/NOE signal is used as NOE and enables half-word and byte reads.

Figure 9. EBI Connection for External 16-bit Memory Device, 16-bit Access Only

In the same configuration as shown in Figure 9 above, it is possible to connect 2x8-bit

memory devices with 16-bit access. The configuration shown in Figure 10 on page 28

demonstrates how to interface the EBI with 2x8-bit memories (for example 2x8-bit ROM

memory) as a 16-bit memory page.

EBI

A[21:1]

NOE

NWE

D[15:0]

16-bit

External Memory

NCS

D[15:0]

A[20:0]

NWE

NOE

NCE

AT91SAM7A2-AI Datasheet(PDF) 27 Page - ATMEL Corporation

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