14
XMEGA A3U [DATASHEET]
Atmel-8386D-AVR-ATxmega64A3U-128A3U-192A3U-256A3U–03/2014
7.8
Data Memory and Bus Arbitration
Since the data memory is organized as four separate sets of memories, the different bus masters (CPU, DMA controller
read and DMA controller write, etc.) can access different memory sections at the same time.
7.9
Memory Timing
Read and write access to the I/O memory takes one CPU clock cycle. A write to SRAM takes one cycle, and a read from
SRAM takes two cycles. For burst read (DMA), new data are available every cycle. EEPROM page load (write) takes one
cycle, and three cycles are required for read. For burst read, new data are available every second cycle. Refer to the
instruction summary for more details on instructions and instruction timing.
7.10
Device ID and Revision
Each device has a three-byte device ID. This ID identifies Atmel as the manufacturer of the device and the device type. A
separate register contains the revision number of the device.
7.11
JTAG Disable
It is possible to disable the JTAG interface from the application software. This will prevent all external JTAG access to the
device until the next device reset or until JTAG is enabled again from the application software. As long as JTAG is
disabled, the I/O pins required for JTAG can be used as normal I/O pins.
7.12
I/O Memory Protection
Some features in the device are regarded as critical for safety in some applications. Due to this, it is possible to lock the
I/O register related to the clock system, the event system, and the advanced waveform extensions. As long as the lock is
enabled, all related I/O registers are locked and they can not be written from the application software. The lock registers
themselves are protected by the configuration change protection mechanism.
7.13
Flash and EEPROM Page Size
The flash program memory and EEPROM data memory are organized in pages. The pages are word accessible for the
flash and byte accessible for the EEPROM.
Table 7-4 on page 14 shows the Flash Program Memory organization and Program Counter (PC) size. Flash write and
erase operations are performed on one page at a time, while reading the Flash is done one byte at a time. For Flash
access the Z-pointer (Z[m:n]) is used for addressing. The most significant bits in the address (FPAGE) give the page
number and the least significant address bits (FWORD) give the word in the page.
Table 7-4.
Number of words and pages in the flash.
Table 7-5 on page 15 shows EEPROM memory organization for the Atmel AVR XMEGA A3U devices. EEEPROM write
and erase operations can be performed one page or one byte at a time, while reading the EEPROM is done one byte at
a time. For EEPROM access the NVM address register (ADDR[m:n]) is used for addressing. The most significant bits in
the address (E2PAGE) give the page number and the least significant address bits (E2BYTE) give the byte in the page.
Devices
PC size
Flash size
Page Size
FWORD
FPAGE
Application
Boot
bits
bytes
words
Size
No of
pages
Size
No of
pages
ATxmega64A3U
16
64K + 4K
128
Z[7:1]
Z[16:8]
64K
256
4K
16
ATxmega128A3U
17
128K + 8K
256
Z[8:1]
Z[17:9]
128K
256
8K
16
ATxmega192A3U
17
192K + 8K
256
Z[8:1]
Z[17:9]
192K
384
8K
16
ATxmega256A3U
18
256K + 8K
256
Z[8:1]
Z[18:9]
256K
512
8K
16