AT91SAM7A2_04 Datasheet, PDF (29/369 Pages) ATMEL Corporation – AT91 ARM Thumb-based Microcontrollers

AT91SAM7A2
Byte Write Access (BAT = 0)
This mode is selected by setting the BAT bit to 0 in AMC_CSRX registers. This is the
mode selected at reset.
In this mode users can interface the EBI with one or two 8-bit memories.
If the EBI is interfaced with two 8-bit memories, then users can choose to have either an
8- or 16-bit access.
The NRD signal is used for reading and two signals are used for writing, NWR0 for lower
byte writes and NWR1 for upper byte writes.
Figure 12 shows how to connect one and two 8-bit memories with the EBI.
The example shown in Figure 13 demonstrates what happens when AT91SAM7A2
boots in this mode on a 16-bit memory (type Flash).
8-bit Access Device Connection A typical 8-bit memory device connection with 8-bit access is shown here.
DBW[1:0] should be set for a 8-bit-data bus width and only NWR0 is used.
• The A0/NLB signal is used as A0.
• The NWR1/NUB signal is not used.
• The NWR0/NWE signal is used as NWR0 and enables lower byte writes.
• The NRD/NOE signal is used as NRD and enables half-word and byte reads.
Figure 12. EBI Connection for External 8-bit Memory Device, 8-bit Access Only
EBI
8-bit
External Memory
D[7:0]
A[21:0]
NWR0
NRD
NCS
D[7:0]
A[21:0]
NWE
NOE
NCE
8-bit or 16-bit Access Device
Connection
A typical 2x8-bit memory device connection with 8-bit or 16-bit access is shown below.
• The A0/NLB signal is not used.
• The NWR1/NUB signal is used as NWR1 and enables upper byte writes.
• The NWR0/NWE signal is used as NWR0 and enables lower byte writes.
• The NRD/NOE signal is used as NRD and enables half-word and byte reads.
6021A–ATARM–07/04
PRELIMINARY
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