Datasheet

262
Atmel | SMART SAM D20 [DATASHEET]
Atmel-42129K–SAM-D20_datasheet–06/2014
To issue a command, the CTRLA.CMD bits must be written along with the CTRLA.CMDEX value. When a command is
issued, INTFLAG.READY will be cleared until the command has completed. Any commands written while
INTFLAG.READY is low will be ignored. Read the CTRLA register description for more details.
The CTRLB register must be used to control the power reduction mode, read wait states and the write mode.
20.6.5.1 NVM Read
Reading from the NVM main address space is performed via the AHB bus by addressing the NVM main address space
or auxiliary address space directly. Read data is available after the configured number of read wait states (CTRLB.RWS)
set in the NVM Controller, has passed.
The number of cycles data are delayed to the AHB bus is determined by the read wait states. Examples of using zero
and one wait states are shown in Figure 20-5.
Figure 20-5. Read Wait State Examples
20.6.5.2 NVM Write
The NVM Controller requires that an erase must be done before programming. The entire NVM main address space can
be erased by a debugger Chip Erase command. Alternatively, rows can be individually erased by the Erase Row
command.
After programming, the region that the page resides in can be locked to prevent spurious write or erase sequences.
Locking is performed on a per-region basis, and so locking a region locks all pages inside the region.
Data to be written to the NVM block are first written and stored in an internal buffer called the page buffer. The page
buffer contains the same number of bytes as an NVM page. Writes to the page buffer must be 16 or 32 bits. 8-bit writes
to the page buffer is not allowed, and will cause a system exception.
Writing to the NVM block via the AHB bus is performed by a load operation to the page buffer. For each AHB bus write,
the address is stored in the ADDR register. After the page buffer has been loaded with the required number of bytes, the
page can be written to the addressed location by setting CMD to Write Page and setting the key value to CMDEX. The
LOAD bit in the STATUS register indicates whether the page buffer has been loaded or not. Before writing the page to
memory, the accessed row must be erased.
By default, automatic page writes are enabled (MANW=0). This will trigger a write operation to the page addressed by
ADDR when the last location of the page is written.
Because the address is automatically stored in ADDR during the I/O bus write operation, the last given address will be
present in the ADDR register. There is no need to load the ADDR register manually, unless a different page in memory is
to be written.
Rd 0 Rd 1 Idle
Data 0 Data 1
1 Wait State
Rd 0
Rd 1
Idle
Data 0 Data 1
0 Wait States
AHB Command
AHB Slave Ready
AHB Slave D ata
AHB Command
AHB Slave Ready
AHB Slave Data