Datasheet

35.7.2 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: byte write or byte
select. This is controlled by the BA
T field of the SMC_MODE register for the corresponding chip select.
35.7.2.1 Byte Write Access
Byte write access is used to connect 2 × 8-bit devices as a 16-bit memory, and supports one 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.
35.7.2.2 Byte Select Access
Byte select access is used to connect one 16-bit device. 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.
Figure 35-4. Connection of 2 × 8-bit Devices on a 16-bit Bus: Byte W
rite 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]
35.7.2.3 Signal Multiplexing
Depending on the byte access type (BAT), only the byte write signals or the byte select signals are used. To save
I/Os at the external bus interface, control signals at the SMC interface are multiplexed. The following table 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 the Byte Select option is selected, NWR1 is unused. When the
Byte W
rite option is selected, NBS0 is unused.
SAM E70/S70/V70/V71 Family
Static Memory Controller (SMC)
© 2019 Microchip T
echnology Inc.
Datasheet
DS60001527D-page 417