Acer AcerNote 970 Service Manual page 39

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Serial port
The serial port is a UART and is contained within the 87366 super I/O chip. The UART
operates off of a 14 Mhz clock. The serial port also has a transceiver, a MAX211. Therefore,
there are several steps to the power conservation of the serial port as below:
1. Disable the UART1 decode in the 87336 chip.
2. Tri-state the UART1 output pins.
3. Assert the Power Down pin[pin-46(SM5_SPPD) of SMC] on the MAX211 chip.
4. Disable the 14Mhz clock (If the floppy and the SIR are also disabled).
Recovery from power down is the opposite procedure.
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SIR (UART)
The SIR port is basically UART. The UART operates off of a 14Mhz clock. The IR port has a
DA converter. The UART2 disable control circuit is within the 87336 chip.
1. Tri-state the UART2 output pins.
2. Assert the power down pin [pin-39(SM5_IRDAPD) of SMC] on the DA converter.
3. Disable the 14Mhz clock (If the floppy and the serial port are also disabled).
Recovery from power down is the opposite procedure.
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Parallel port
The video chip does have an activity pin (pin-75, ACTIVITY), used
to detect activity to the video itself. This pin is used as a speed-up
event for the CPU and the determination of software suspend.
The MAX211 chip will still pass through the Ring Indicate signal
even while in the power down mode(if the Resume On Modem Ring
in BIOS Setup is set to enabled). .
If the 14Mhz is disabled through the 87336 power down mode, then
all serial and floppy functions will fail.
If the 14Mhz is disabled through the National power down mode,
then all serial and floppy functions will fail.