NXP Semiconductors Lite5200B, Руководство пользователя, Страница: 34 / 138

Hardware Description
LITE5200B User’s Manual, Rev. 0
4-20 Freescale Semiconductor
mode instead of a cold power up. The system software in the MPC5200B should detect this condition and
restore context to return to the operational state. After the MPC5200B has restored context it should then
drive the "PWR_DN_CTL_STS" net high for 10 uS to indicate that it has recovered context. This is done
by configuring MPC5200B port PSC2_4 as an output with a data out value of "1". In response the QT1
will also drive the net high through R208. After driving the "PWR_DN_CTL_STS" net high for 10 uS the
MPC5200B should reconfigure port PSC2_4 as an input with interrupt sense capability so that it can detect
any future external power down requests. The QT1 will continue to drive the net high through R208 until
an external request is received or the MPC5200B requests another power down. This restores the power
control circuit to its normal power state.
Note that a full power down of the board by removing the primary 5V supply while in low power mode
will cause a cold reset when power is restored.)
4.6.4.7 Disabling Power Down
It may be desirable to use MPC5200B port PSC2_4 for an alternate function. If this is required, the zero
ohm resistor at R88 should be removed. This disconnects the net "PWR_DN_CTL_STS" from the
MPC5200B. It is not necessary to drive this net high since the QT1 is driving the net high through R208.