Maxim DS87C530 Clock User Manual

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DS87C530/DS83C530 EPROM/ROM Microcontrollers with Real-Time Clock

17 of 47

POWER MANAGEMENT

Along with the standard Idle and power-down (Stop) modes of the standard 80C52, the

DS87C530/DS83C530 provide a new Power Management Mode. This mode allows the processor to

continue functioning, yet to save power compared with full operation. The DS87C530/DS83C530 also

feature several enhancements to Stop mode that make it more useful.

POWER MANAGEMENT MODE (PMM)

Power Management Mode offers a complete scheme of reduced internal clock speeds that allow the CPU

to run software but to use substantially less power. During default operation, the DS87C530/DS83C530

use four clocks per machine cycle. Thus the instruction cycle rate is (Clock/4). At 33MHz crystal speed,

the instruction cycle speed is 8.25MHz (33/4). In PMM, the microcontroller continues to operate but uses

an internally divided version of the clock source. This creates a lower power state without external

components. It offers a choice of two reduced instruction cycle speeds (and two clock sources - discussed

below). The speeds are (Clock/64) and (Clock/1024).

Software is the only mechanism to invoke the PMM. Table 4 illustrates the instruction cycle rate in PMM

for several common crystal frequencies. Since power consumption is a direct function of operating speed,

PMM 1 eliminates most of the power consumption while still allowing a reasonable speed of processing.

PMM 2 runs very slowly and provides the lowest power consumption without stopping the CPU. This is

illustrated in Table 5.

Note that PMM provides a lower power condition than Idle mode. This is because in Idle, all clocked

functions such as timers run at a rate of crystal divided by 4. Since wake-up from PMM is as fast as or

faster than from Idle and PMM allows the CPU to operate (even if doing NOPs), there is little reason to

use Idle mode in new designs.

Table 4. Machine Cycle Rate

CRYSTAL SPEED

(MHz)

FULL OPERATION

(4 CLOCKS)

(MHz)

PMM1

(64 CLOCKS)

(kHz)

PMM2

(1024 CLOCKS)

(kHz)

11.0592 2.765 172.8 10.8

16 4.00 250.0 15.6

25 6.25 390.6 24.4

33 8.25 515.6 32.2

Table 5. Typical Operating Current in PMM

CRYSTAL SPEED

(MHz)

FULL OPERATION

(4 CLOCKS)

(mA)

PMM1

(64 CLOCKS)

(mA)

PMM2

(1024 CLOCKS)

(mA)

11.0592 13.1 5.3 4.8

16 17.2 6.4 5.6

25 25.7 8.1 7.0

33 32.8 9.8 8.2

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Maxim DS87C530 Clock User Manual