RAM
active
RAM
active
RAM in
retention
RAM
off
Active
Mode
Active
Mode
LPM3 or
LPM4
RCRSyOFF0 = 0
RC
RSyO
FF0
= 1
RAM Controller (RAMCTL) Introduction
332
SLAU367P – October 2012 – Revised April 2020
Copyright © 2012–2020, Texas Instruments Incorporated
RAM Controller (RAMCTL)
10.1 RAM Controller (RAMCTL) Introduction
The RAM Controller allows reduction of the leakage current during LPM3 and LPM4. The RAM is
partitioned in one to four sectors, depending on the device. See the device-specific data sheet for sector
allocation and size.
10.2 RAMCTL Operation
Each sector y is controlled by a sector off control bit (RCRSyOFF0) in the RAM Controller Control Register
0 (RCCTL0). By default, the RAM content is retained in LPM3 and LPM4 (RCRSyOFF0 = 0).
By setting the RAM sector's control bit RCRSyOFF0 to 1, the respective RAM sector is powered down
completely during LPM3 and LPM4 and all RAM content within the sector y is lost after a wake-up from
LPM3 or LPM4. After wake-up the RAM can be accessed normally.
shows the possible transitions when entering LPM3 or LPM4 and when waking up from LPM3
or LPM4.
NOTE:
After a wake-up from LPM3 and LPM4 with RCRSyOFF0 = 1, the content of powered down
sectors is lost and completely undefined. Any potentially required re-initialization must be
implemented in software.
The RCCTL0 register is protected with a key. The RCCTL0 register content can be modified only if the
correct key is written during a word write. Byte write accesses or write accesses with a wrong key are
ignored.
Figure 10-1. RAM Power Mode Transitions Into and Out of LPM3 or LPM4
10.2.1 Considerations for Complete Power Down
Using the power-down feature requires special care in devices with only one RAM sector or if all sectors
are powered down. Usually the program stack is located in RAM; therefore, using the power-down (with
RCRSyOFF0 = 1) destroys the stack content when entering LPM3 or LPM4. This is acceptable if the stack
is empty when entering LPM3 or LPM4; otherwise, the stack must be located in a different memory (for
example, FRAM).
10.2.2 DACCESSIE and DACCESSIFG Bits in RCCTL1 Register
This section applies only to the devices that include both the USS and the LEA modules. The LEA RAM
can be accessed by CPU, DMA, or DTC. Among the three bus master sources, the DTC has the highest
priority. The DTC is the data transfer controller in the SDHS, which is a submodule of the USS module.
The DTC transfers data from the SDHS directly to the LEA RAM. It is highly recommended not to access
LEA RAM while the DTC is active. If CPU or DMA accesses the LEA RAM while the DTC is accessing the
same memory:
•
A write access from CPU or DMA is ignored