22-6
MPC561/MPC563 Reference Manual
MOTOROLA
Modes of Operation
22.4.4
Standby Operation/Keep-Alive Power
The registers and control logic for the CALRAM module are powered by VDD. The
memory array is also supplied by VDD during normal operation; however, when the VDD
is off, the CALRAM array is backed up by a switched source (IRAMSTBY) that is also
known as standby power.
22.4.5
Stop Operation
The low power stop mode for this module is entered by setting the disable bit (DIS) in the
CRAMMCR register. Reads from and writes to the array during this mode will generate an
error.
When the disable bit (DIS) is cleared, the module returns to normal function.
22.4.6
Overlay Mode Operation
For a microcontroller used as a controller for an engine (or other electromechanical device),
various parameters stored in the Flash memory may need to be changed in order to properly
tune (calibrate) the engine. Because Flash memory may not be readily programmed during
normal operation of an embedded controller, portions of the CALRAM array can be
overlayed onto the U-bus Flash memory. By allowing the CALRAM module to overlay
portions of Flash memory, parameters normally stored in the Flash may be tweaked and
changed with a development tool both during normal operation and prior to programming
a final, more precise version of the Flash memory.
The overlay is for read-only data and does not affect instruction fetches from the Flash. The
data for any L-bus address which falls in the overlay region of the U-bus Flash will be
driven by the CALRAM on the L-bus. The CALRAM also indicates to the L2U to block
the data from the Flash to be driven onto the L-bus. As far as the RCPU core is concerned,
the timing of data coming from the CALRAM appears to be the same as that from the Flash.
22.4.6.1 Overlay Mode Configuration
Each CALRAM module contains eight overlay regions, each of which is 512 bytes long as
shown in
Figure 22-4. All overlay regions of a module are contiguous and each starts at the
least significant address of the region and can increment all the way up to 512 bytes as
the base addresses RBA[11:29] of the U-bus Flash regions and the RGN_SIZE[0:4] to be
overlaid. Note that each region can also be individually disabled by writing 0000 to
RGN_SIZE[0:3]. If the programmed base address is not naturally aligned with respect to
the RGN_SIZE field, the least significant bits of the base address fields can be considered
0’s in order to make the starting address naturally aligned. In an RBA register,