Maxim Integrated MAXQ Family Users Guide: MAXQ2000 Supplement - Manual (Page 17)

Power Management Features
The MAXQ2000 provides the following features to assist in power management.
• Divide-by-256 (PMM1) and 32kHz (PMM2) modes to reduce current consumption.
• Switchback mode to exit PMM modes automatically when rapid processing is required.
• Ultra-low-power Stop mode.
Table 3 shows the system registers and bits used to control power management features. For more information, refer to the register
descriptions in the MAXQ Family User’s Guide.
Table 3. System Power Management Registers
Divide-by-256 Mode (PMM1)
In this power management mode, all operations continue as normal but at a reduced clock rate (the high-frequency system clock divid-
ed by 256). This power management mode affects module clock rates as follows.
• Program execution occurs at the high-frequency clock rate divided by 256.
• The RTC module continues to operate using its originally selected clock, which is either the 32kHz clock or the high-frequency clock
divided by 128, as selected by the ACS bit (RCNT.13).
• The LCD module continues to operate using its originally selected clock, which is either the 32kHz clock or the high-frequency clock
divided by 128, as selected by the LCCS bit (LCRA.6).
• All other functional modules (timers, UARTs, SPI) operate at the high-frequency clock rate divided by 256.
MAXQ Family User’s Guide:
MAXQ2000 Supplement
CLOCK
RESET
RESET
SAMPLING
INTERNAL
RESET
FIRST
INSTRUCTION
FETCH
Figure 7. MAXQ2000 External Reset
REGISTER ADDRESS BIT FUNCTION
CKCN M8[0Eh] [1:0] to CD[1:0]
Selects clock divide-by-1 (00), -2 (01), -4 (10), or -8 (11) mode. When PMM mode is
enabled, selects divide-by-256 (00) or 32kHz (11) mode.
CKCN M8[0Eh] 2 (PMME) Selects PMM mode (when set to 1) or normal clock divide mode (when set to 0).
CKCN M8[0Eh] 3 (SWB)
When set to 1, enables automatic switchback from PMM (divide-by-256 mode) to normal
clock divide mode under certain conditions.
CKCN M8[0Eh] 4 (STOP) When set to 1, causes the processor to enter Stop mode.
Maxim Integrated 17