33.2.4.3 CTRLB SFR Description

The CTRLB fields can be changed at anytime, provided the FCR is not write protected. Updates that affect the cache happen on read access boundaries.

The Register values for CTRLB are discussed below.

PRM - Power Reduction Mode

The PRM field allows the user to manually control the Flash power mode. Writing CTRLB.PRM to a 1 toggles the power reduction mode. The current mode is reflected in STATUS.PRM. When in Flash Hibernate the panel wakes up on access but does not return to Flash Hibernate. Note that when awake the Flash reenters Auto Standby if not accessed for one read cycle time.

To change the Flash Power Reduction Mode:

  1. Read current PRM value. curr_prm = STATUS.PRM.
  2. Write 0x01 to BYTE 0 of CTRLB (toggle Flash Power mode).
  3. Wait until STATUS.PRM toggles. while (curr_prm == STATUS.PRM) {}.

No flags get set nor are interrupts generated from a power reduction mode change. The power status of the Flash is reflected in STATUS.PRM.

Note: Changing the Power Reduction Mode incurs a delay of TDPDH to take effect.

SLP[1:0] - Power Mode in Standby Sleep

The SLP field controls the Power Reduction Mode during System Standby, Sleep. Waking the Flash from its power down mode takes at least TDPDH. Upon system wakeup, the current Power Reduction Mode is reflected in STATUS.PRM. See the SLP SFR field for more details.