Datasheet

SAM3X / SAM3A [DATASHEET]
Atmel-11057C-ATARM-SAM3X-SAM3A-Datasheet_23-Mar-15
426
25.9.2.2 Byte Select Access
In this mode, read/write operations can be enabled/disabled at byte level. One byte-select line per byte of the data
bus 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.
Byte Select Access is used to connect one 16-bit device.
Figure 25-6. Connection of 2 x 8-bit Devices on a 16-bit Bus: Byte Write Option
25.9.2.3 Signal Multiplexing
Depending on the byte access type (BAT), only the write signals or the byte select signals are used. To save IOs at
the external bus interface, control signals at the SMC interface are multiplexed. Table 25-5 shows signal
multiplexing depending on the data bus width and the byte access type.
For 16-bit devices, bit A0 of address is unused. When Byte Select Option is selected, NWR1 is unused. When Byte
Write option is selected, NBS0 is unused.
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]
Table 25-5. SMC Multiplexed Signal Translation
Signal Name 16-bit Bus 8-bit Bus
Device Type 1x16-bit 2 x 8-bit 1 x 8-bit
Byte Access Type (BAT) Byte Select Byte Write
NBS0_A0 NBS0 A0
NWE_NWR0 NWE NWR0 NWE
NBS1_NWR1 NBS1 NWR1
A1 A1 A1 A1