
200
42073A-MCU Wireless-02/13
ATmega2564/1284/644RFR2
power supply) and all its data are lost. The typical voltage reduction levels are shown in
the following table.
Table 12-106 DRTMP Register Bits
Register Bits
Value
Description
DRTMP1:0
0
500 mV
1
425 mV
2
360 mV
3
< 5 mV
Bit 1:0 – DRTMN1:0 - Negative Data Retention Voltage Setting
The bits DRTMN1:0 define the reduction of the negative supply voltage during data
retention (DRT) mode. A preprogrammed calibration value is automatically written to
this register during chip reset, giving the factory value. The DRT mode must be enabled
by setting ENDRT high. Otherwise the SRAM is switched off (disconnected from the
power supply) and all its data are lost. The typical voltage reduction levels are shown in
the following table.
Table 12-107 DRTMN Register Bits
Register Bits
Value
Description
DRTMN1:0
0
525 mV
1
415 mV
2
325 mV
3
< 5 mV
12.6.8 DRTRAM2 – Data Retention Configuration Register #2
Bit
7
6
5
4
3
2
1
0
NA ($133)
DISPC
Res
DRTSWOK
ENDRT
DRTMP1 DRTMP0 DRTMN1 DRTMN0 DRTRAM2
Read/Write
RW
R
RW
Initial Value
0
The DRTRAM2 register controls the behavior of SRAM block #2 (ATmega256RF block
#4 and #5 in parallel) in the power-states "power-save" and "power-down". To prevent
any data loss the SRAM will not completely disconnected from the power supply.
Reserved bits will be overwritten during chip reset by the factory calibration and should
not be modified.
Bit 7 – DISPC - Disable Power-chain of SRAM 2
This bit allows to temporarily disable the power-chain of the SRAM block #2
(ATmega256RF block #4 and #5 in parallel) . In this way the block can be put into data
retention (DRT) mode to measure the DRT voltage levels. See section "SRAM DRT
Voltage Measurement" for details.
Bit 6 – Res - Reserved Bit
This bit is reserved for future use. A read access always will return zero. A write access
does not modify the content.
Bit 5 – DRTSWOK - DRT Switch OK
This bit indicates the status of the SRAM power-switch. A logical one indicates that the
SRAM supply voltage is fully available and the memory may be accessed normally.