AT91M40400-25C ATMEL Corporation, AT91M40400-25C Datasheet - Page 12

• Manufacturer Part Number: AT91M40400-25C
• Description: 16/32-bit Microcontroller, 2.7V to 3.6V Operating Range
• Manufacturer: ATMEL Corporation

Data Bus Width
A data bus width of 8 or 16 bits can be selected for each
chip select. This option is controlled by the DBW field in the
EBI_CSR (Chip Select Register) for the corresponding chip
select.
Figure 8 shows how to connect a 512K x 8-bit memory on
NCS2.
Figure 8. Memory Connection for an 8-Bit Data Bus
Figure 9 shows how to connect a 512K x 16-bit memory on
NCS2.
Figure 9. Memory Connection for a 16-Bit Data Bus
EBI
EBI
12
D8 - D15
A1 - A19
D0 - D7
D8 - D15
A1 - A18
NCS2
D0 - D7
NWE
NWR1
NWR0
NUB
NOE
NLB
NCS2
NRD
A0
AT91M40400
D0 - D7
D8 - D15
A0 - A18
Low Byte Enable
High Byte Enable
Write Enable
Output Enable
Memory Enable
D0 - D7
A1 - A18
A0
Write Enable
Output Enable
Memory Enable
Byte Write or Byte Select Access
Each chip select with a 16-bit data bus can operate with
one of two different types of write access:
•
•
This option is controlled by the BAT field in the EBI_CSR
(Chip Select Register) for the corresponding chip select.
Byte Write Access is used to connect 2 x 8-bit devices as a
16-bit memory page.
•
•
•
•
Figure 10 shows how to connect two 512K x 8-bit devices
in parallel on NCS2.
Figure 10. Memory Connection for 2 x 8-Bit Data Busses
Byte Select Access is used to connect 16-bit devices in a
memory page.
•
•
EBI
Byte Write Access supports two byte write and a single
read signal.
Byte Select Access selects upper and/or lower byte with
two byte select lines, and separate read and write
signals.
The signal A0/NLB is not used.
The signal NWR1/NUB is used as NWR1 and enables
upper byte writes.
The signal NWR0/NWE is used as NWR0 and enables
lower byte writes.
The signal NRD/NOE is used as NRD and enables half-
word and byte reads.
The signal A0/NLB is used as NLB and enables the
lower byte for both read and write operations.
The signal NWR1/NUB is used as NUB and enables the
upper byte for both read and write operations.
D8 - D15
A1 - A19
D0 - D7
NWR1
NWR0
NCS2
NRD
A0
D0 - D7
A0 - A18
Write Enable
Read Enable
Memory Enable
D8 - D15
A0 - A18
Write Enable
Read Enable
Memory Enable