
202
42073A-MCU Wireless-02/13
ATmega2564/1284/644RFR2
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.
Bit 4 – ENDRT - Enable SRAM Data Retention
During "Deep-Sleep" each SRAM block will either be switched off or provides data
retention of its memory content. This bit must set to one if data retention mode should
be used. Otherwise the SRAM is switched off (disconnected from the power supply)
and all its data are lost.
Bit 3:2 – DRTMP1:0 - Positive Data Retention Voltage Setting
The bits DRTMP1:0 define the reduction of the positive 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 12-110 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 12-111 DRTMN Register Bits
Register Bits
Value
Description
DRTMN1:0
0
525 mV
1
415 mV
2
325 mV
3
< 5 mV
12.6.10 LLCR – Low Leakage Voltage Regulator Control Register
Bit
7
6
5
4
3
2
1
0
NA ($12F)
Res1
Res0
LLDONE LLCOMP
LLCAL
LLTCO
LLSHORT LLENCAL
LLCR
Read/Write
R
RW
Initial Value
0
1
This register allows to monitor and to control the calibration process of the low-leakage
voltage regulator. The automatic calibration is the normal operation mode. However,
certain circumstances may require to disable this automatic process for instance to
save power-up time. The results of the automatic calibration can also be modified when
required by the application for instance to get a higher or lower output voltage.