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Applications Information
MOTOROLA
MC68307 USER’S MANUAL
10-7
10.2 POWER MANAGEMENT
The fully static MC68307 has a number of flexible power management features that enable
the power consumption to be minimized for different applications. This section describes
how to use these features to best effect in reducing overall system power consumption.
10.2.1 Fully Static Operation
The MC68307 is fully static; this means that the clock to the device can be stopped com-
pletely without causing damage. In addition the clock can be restarted with no loss of status
occurring.
These two fundamental benefits of fully static operation are utilized in the MC68307 power
management features. The MC68307 allows the clocks to different modules within the
device to be stopped under software control in order to minimize power consumption for a
particular user application. The external clock input can also be varied in frequency between
DC (i.e., stopped externally) and the maximum operating frequency (16.67 MHz).
By setting the appropriate bits in the configuration register (MBCD, TMCD, UACD, CKD and
LPEN), the internal clocks to the M-bus, timer, UART, CLKOUT and CPU can be individually
stopped. With the exception of the CPU, these clocks can all be restarted by clearing the
corresponding bit in the configuration register. When a module clock is turned off, the mod-
ule current consumption is reduced to very low leakage levels.
Table 10-1 gives typical percentage power savings that can be made by stopping the clocks
to modules that are not used in a particular operating mode. These figures are from mea-
surements taken on a development board. They represent percentages of full operating
power consumption and are averages over four different test cases (16.67MHz and 8MHz
at 5V and 3.3V).
Table 10-1. Power Contribution from Modules
Module
Percentage IDD
All Operational
100%
CLKOUT
5%
M-bus
6%
Timer
7%
UART
15%
CPU (EC000)
61%
Low-Power Sleep
6%