
1-12
Power Management
As a concrete example, consider the previous example, which has several peripheral
devices (floppy disk drive, serial port, etc.). Suppose the following peripheral-power-man-
agement scheme is to be implemented:
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10 s of inactivity—Turn off the floppy disk drive
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10 min of inactivity—Turn off the serial port transceiver
This scheme can be implemented by using Doze mode to signal the floppy disk drive, and
Sleep or Suspend mode to signal the transceiver. The PMC pins can be programmed to
provide this control through the Power Control 1–4 registers at Indexes 80–81h and
AB–ACh.
The settings shown in Table 1-4 on page 1-12 provide the following scheme:
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PMC1 is activated when the system is in High-Speed PLL or Low-Speed PLL mode
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PMC2 is activated when the system is in Doze mode
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PMC3 is activated when the system is in Sleep mode
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PMC4 is activated when the system is in Suspend mode
The designer can use the PMC4–PMC2 pins to disable the floppy disk drive and the
transceiver.
A more elaborate system permits the control of each peripheral on an individual basis.
The settings shown in Table 1-5 on page 1-12 extend the PMC initialization example to
show how to power down an external device after 8 s. The following example shows how
the élanSC310 microcontroller can be programmed to make the PMC1 pin change state
after 8 s of system inactivity. The designer can use this signal to turn off power to the
external device.
Table 1-4
Power-Management Control Pin Settings
Instruction
Ports
Index and Data
Comment
IOW
IOW
022h
023h
ACh
0001 0000
Activate PMC1 when in High-Speed PLL or Low-Speed
PLL mode.
IOW
IOW
022h
023h
80h
0100 0000
Activate PMC2 when in Doze mode.
IOW
IOW
022h
023h
ABh
1000 1011
Activate PMC3 when in Sleep mode and activate PMC4
when in Suspend mode.
Table 1-5
PIO Timeout Settings
Instruction
Ports
Index and Data
Comment
IOW
IOW
022h
023h
45h
1100 000
Set PIO address to the window at port 300h.
IOW
IOW
022h
023h
46h
0100 0110
Set the I/O window size to 8 bytes and the timeout to 8 s.