Atmel ARM-Based Evaluation Kit AT91SAM9N12-EK AT91SAM9N12-EK Data Sheet
Product codes
AT91SAM9N12-EK
376
SAM9N12/SAM9CN11/SAM9CN12 [DATASHEET]
11063K–ATARM–05-Nov-13
30.8.2.1 Byte Write Access
Byte write access supports one byte write signal per byte of the data bus and a single read signal.
Note that the SMC does not allow boot in Byte Write Access mode.
For 16-bit devices: the SMC provides NWR0 and NWR1 write signals for respectively byte0 (lower byte) and byte1
(upper byte) of a 16-bit bus. One single read signal (NRD) is provided.
(upper byte) of a 16-bit bus. One single read signal (NRD) is provided.
Byte Write Access is used to connect 2 x 8-bit devices as a 16-bit memory.
For 32-bit devices: NWR0, NWR1, NWR2 and NWR3, are the write signals of byte0 (lower byte), byte1, byte2 and
byte 3 (upper byte) respectively. One single read signal (NRD) is provided.
byte 3 (upper byte) respectively. One single read signal (NRD) is provided.
Byte Write Access is used to connect 4 x 8-bit devices as a 32-bit memory.
Byte Write option is illustrated on
.
30.8.2.2 Byte Select Access
In this mode, read/write operations can be enabled/disabled at a byte level. One byte-select line per byte of the data bus
is provided. One NRD and one NWE signal control read and write.
is provided. One NRD and one NWE signal control read and write.
For 16-bit devices: the SMC provides NBS0 and NBS1 selection signals for respectively byte0 (lower byte) and
byte1 (upper byte) of a 16-bit bus.
byte1 (upper byte) of a 16-bit bus.
Byte Select Access is used to connect one 16-bit device.
For 32-bit devices: NBS0, NBS1, NBS2 and NBS3, are the selection signals of byte0 (lower byte), byte1, byte2
and byte 3 (upper byte) respectively. Byte Select Access is used to connect two 16-bit devices.
and byte 3 (upper byte) respectively. Byte Select Access is used to connect two 16-bit devices.
shows how to connect two 16-bit devices on a 32-bit data bus in Byte Select Access mode, on NCS3 (BAT =
Byte Select Access).
Figure 30-6. Connection of 2 x 8-bit Devices on a 16-bit Bus: Byte Write Option
SMC
A1
NWR0
NRD
NCS[3]
Write Enable
Read Enable
Memory Enable
NWR1
Write Enable
Read Enable
Memory Enable
D[7:0]
D[7:0]
D[15:8]
D[15:8]
A[24:2]
A[23:1]
A[23:1]
A[0]
A[0]